BIOLOGY 

LIBRARY 

G 


HUMAN  PHYSIOLOGY: 


DESIGNED     FOR 


COLLEGES  AND  THE  HIGHER  CLASSES  IN  SCHOOLS, 


FOR  GENERAL  READING. 


BY  WORTHINGTON  HOOKER,  M.  D., 

PROFESSOR   OF  THE  THEORY   AND  PRACTICE   OF  MEDICINE  IN   YALJC  COI 

AUTHOR  OF   "PHYSICIAN  AND  PATIENT." 


Illustrated  by  nearly  200  Engravings. 


NEW    Y  O  E  K : 

PRATT,    OAKLEY    &    COMPANY, 
21    MURRAY    STREET. 


R1OLOGY 


ENTERED,  according  to  Act  of  Congress,  in  the  year  of  our  Lord. 
One  thousand  eight  hundred  and  fifty-four, 

BY  WORTIIIXGTOX  HOOKER.  M   D., 
In  the  C'erk's  Office  of  the  District  Court  of  Connecticut. 


CONTENTS. 


PART    I. 

CHAPTER  I.  PA3K. 

ORGANIZED  AND  UNORGANIZED  SUBSTANCES.         .        .         .13 

CHAPTER  II. 
THE  DISTINCTION  BETWEEN  ANIMALS  AND  PLANTS.         .  21 

CHAPTER  III. 

MAN  IN  HIS  RELATIONS  TO  THE  THREE  KINGDOMS  OF  NA- 
TURE,           27 

PART    II. 

CHAPTER  IV. 
GENERAL  VIEWS  or  PHYSIOLOGY.  WITH  A  BRIEF  ACCOUNT 

OK    SOME    OF    THE    STRUCTURES    OF    THE    BODY,  .  35 

CHAPTER  V. 
DIGESTION,          .........       42 

CHAPTER  VI. 
CIRCULATION  OF  THE  BLOOD,          .         .         .        .  64 

CHAPTER  VII. 
RESPIRATION, 86 

CHAPTER  VIII. 
FORMATION  AND  REPAIR, 109 

CHAPTER  IX. 
CELL  LIFE, 123 


IV  CONTENTS. 


PART    III. 

THE 

CHAPTER  X. 

PAGE. 
139 

THE 

CHAPTER  XL 
BONES,    

170 

THE 

CHAPTER  XII. 
MUSCLES,  

196 

THE 

CHAPTER  XIII. 
LANGUAGE  OF  THE  MUSCLES,          .... 

222 

THE 

CHAPTER  XIV. 
VOICE,       

243 

THE 

CHAPTER  XV. 
EAR,       

271 

THE 

CHAPTER  XVI. 
EYE,          

287 

CHAPTER  XVII. 
CONNECTION  OF  THE  MIND  WITH  THE  BODY,         .        . '      318 

CHAPTER  XVIII. 
DIFFERENCES  BETWEEN  MAN  AND  THE  INFERIOR  ANIMALS,     347 

CHAPTER  XIX. 
VARIETIES  OF  THE  HUMAN  RACE, 367 

CHAPTER  XX. 
LIFE  AND  DEATH, 381 

CHAPTER  XXL 
HYGIENE,  , 390 

APPENDIX, ...    411 


PREFACE. 


I  HAVE  aimed  so  to  write  this  book,  that  it  shall  be  fitted  both  for  gen- 
eral reading,  and  for  instruction.  It  is  designed  for  the  family  as  well  as 
for  the  school.  It  seemed  desirable  that  these  two  objects  should  be  ao 
complished  at  the  same  time,  and  I  have  not  found  them  to  be  at  all  in- 
compatible. The  instruction  needed  by  the  family  on  this  subject,  differs 
not  from  that  which  is  required  in  the  school-room,  either  in  regard  to 
the  facts  to  be  communicated,  or  the  manner  in  which  it  should  be  done. 
No  one  will  question  the  truth  of  this,  so  far  as  the  facts  are  concerned. 
But  it  is  true  even  as  to  the  mode  of  communicating  them.  In  both  cases 
there  need  to  be  clearness  in  statement,  and  fullness  of  illustration.  Actual 
instruction  is  to  be  given  in  both  cases,  and  to  minds  that  are  very  nearly 
in  the  same  attitude.  I  could  not,  therefore,  see  the  necessity  of  writing  a 
book  on  this  subject  for  the  people  which  should  differ  from  one  written 
for  the  school.  Besides,  it  has  seemed  to  me  desirable  that  there  should 
be  a  greater  community  of  interest  between  the  school  and  the  family  than 
as  yet  exists ;  and  this  object  books  equally  interesting  to  both  will  tend 
to  promote. 

It  may  be  proper  for  me  to  say  a  word  in  relation  to  the  style  of  the 
work.  I  have  adopted  the  style  of  the  lecture-room,  because,  that  while 
it  is  not  inconsistent  with  conciseness,  it  is  the  more  natural  mode  of  in- 
struction, especially  when  so  much  reference  is  made  to  illustrative  figures. 
It  has  enabled  me  also  to  keep  in  view  more  effectually  the  attitude  of  the 
minds  I  address.  I  have  had  my  readers  before  me  continually  as  an 
imaginaiy  audience.  I  have  avoided  technical  terms  as  far  as  possible. 
Whenever  they  are  used  they  are  sufficiently  explained  at  the  time,  so 
that  no  glossary  is  needed.  Some  points  commonly  considered  hard  to 
be  understood  are  treated  of,  but  I  have  endeavored  to  simplify  them,  by 


VI  PKEFACE. 


full  illustration,  and  by  a  presentation  of  the  truth  uncomplicated  with 
speculations  and  hypotheses.  And  these  points  are  so  introduced,  that 
the  mind  is  prepared  by  the  previous  investigation  to  understand  them. 
I  have  aimed  so  to  arrange  the  topics,  as  to  have  a  preparation  constantly 
going  on  in  the  mind  of  the  student,  fitting  him  for  the  proper  under- 
standing of  what  is  to  come  after.  By  this  natural  gradation  in  the  de- 
velopment of  the  whole  subject  some  of  the  deep  things  in  Physiology 
can  be  made  clear,  which  it  would  otherwise  be  impossible  for  the  student 
to  understand.  It  is  proper  to  state  here,  that  I  intend  to  prepare  a  worK 
for  younger  scholars,  in  which  some  of  the  simple  points  in  Physiology 
will  be  illustrated.  This,  by  familiarizing  their  minds  with  the  subject, 
will  fit  them  for  a  more  thorough  understanding  of  the  present  work. 

Although  Physiology  is1  becoming  a  prominent  study  in  the  schools  and 
colleges  in  some  parts  of  our  country,  its  importance  is  no  where  as  yet 
appreciated  as  it  should  be.  It  should  be  made  a  regular  branch  in  our 
Educational  System.  This  has  been  already  done  in  France.  "  A  com- 
petent knowledge,"  says  Carpenter,  "  of  Animal  Physiology  and  Zoology 
is  there  required  from  every  candidate  for  University  honors ;  and  men 
of  the  highest  scientific  reputation  do  not  think  it  beneath  them  to  write 
elementary  books,  for  the  instruction  of  the  beginner." 

The  importance  of  Physiology  as  a  study,  will  appear  from  various  con* 
siderations. 

Many  of  the  subjects  comprised  in  Physiology  have,  in  the  case  of 
most  students,  been  already  studied  in  a  different  phase,  or  mode,  in  other 
branches.  Thus,  if  the  student  has  attended  to  the  Mechanical  Powers 
in  his  Natural  Philosophy,  he  finds  in  the  human  body  the  principles  of 
the  pulley  and  the  lever  illustrated  in  great  variety  and  perfection.  The 
principles  in  relation  to  strength  in  the  form  and  arrangement  of  struc- 
ture he  sees  exemplified  in  the  frame-work  of  the  body  in  the  most  ad- 
mirable manner.  If  he  has  studied  Hydraulics,  he  sees  in  the  body  the 
most  perfect,  and  at  the  same  time  the  most  complicated  hydraulic  ma- 
chinery, working  incessantly  throughout  life  in  the  circulation  of  the 
blood.  The  principles  of  Pneumatics  he  finds  applied  in  the  respiration — 
those  of  Optics  in  the  eye — those  of  Acoustics  in  the  ear — and  those  of 
Musical  Sounds  in  the  apparatus  of  the  voice.  And  then,  his  chemical 


PKEFACE.  VII 

knowledge  meets  with  new  applications  in  his  observation  of  the  changes 
and  the  processes  going  on  in  the  body. 

The  relations,  then,  of  Physiology  to  some  of  the  common  branches 
taught  in  the  higher  classes  in  schools,  are  of  the  most  intimate  charac- 
ter. Physiology,  in  part,  merely  extends  these  branches  into  a  new  and 
interesting  field  ;  and  the  student  who  has  once  entered  this  field  recurs 
to  these  same  branches  with  a  renewed  interest.  Hydraulics,  Pneuma- 
tics, Optics,  &c.,  have  now  a  new  attraction  for  him,  from  this,  to  him 
novel,  application  of  their  principles.  The  interest  thus  awakened  in 
his  mind  is  worth  much  in  itself,  aside  from  the  mere  addition  made  to 
his  knowledge.  And  the  interest  is  enhanced  by  the  consideration,  that 
in  the  human  body  he  sees  the  applications  of  these  principles  to  mechan- 
ism that  exhibits  the  skill  of  perfect  wisdom  and  almighty  power. 

But  there  are  relations  of  Physiology  to  still  other  studies  which  should 
be  noticed. 

The  analogies  that  exist  between  the  human  body  and  all  other  living 
things,  in  relation  to  structure  and  growth,  are  numerous  and  striking. 
Though  life  is  so  diverse  in  its  processes  and  in  the  forms  which  we  see 
it  evolve  in  the  whole  range  of  animated  nature,  it  in  some  important  re- 
spects displays  a  great  similarity,  which  it  is  interesting  to  trace  through- 
out its  diversified  manifestations.  Growth,  or  nutrition,  as  you  will  see 
in  the  following  pages,  is  essentially  the  same  in  the  Plant  as  it  is  in  the 
Animal.  Botany,  therefore,  taught  as  it  should  be,  has  quite  an  intimate 
relation  to  Animal  Physiology.  The  Science  of  Life  is,  in  many  respects, 
one  Science ;  and  if,  in  studying  any  of  its  subdivisions,  we  fail  to  take 
this  broad  view  of  it,  and  to  trace  out  the  analogies  referred  to,  we  lose  a 
large  part  of  the  interest  of  the  study.  Human  Physiology,  the  subject 
of  study  in  this  book,  is  but  a  part  of  a  science  which  offers  to  the  student 
wide  fields  of  observation  exceedingly  diversified  and  full  of  interest. 
This  being  so,  I  could  not  avoid  in  the  following  pages  making  occasional 
reference  to  the  analogies  existing  between  the  phenomena  of  life  as  ex- 
hibited in  the  human  system,  and  those  which  we  see  in  the  living  world 
around  us.  So  that  as  the  student  proceeds  with  the  study,  he  will  find 
himself  interested  in  the  phenomena  of  life  in  whatever  form  they  are 


VU1  PREFACE. 


This  leads  me  to  say  that  this  study  of  nature,  in  its  broad  common  re- 
lations and  its  beautiful  and  extensive  analogies,  should  be  made  very 
prominent  in  our  systems  of  education.  It  is  the  application  of  the  prin- 
ciples of  abstract  science  to  the  forms,  and  especially  the  living  forms  of 
nature  all  about  us,  that  gives  interest  to  these  principles,  and  makes  us 
to  understand  and  appreciate  them.  It  is  here  that  we  find  a  very  seri- 
ous defect  in  the  prevalent  mode  of  education,  even  at  the  present  time, 
notwithstanding  all  our  improvements.  Let  us  look  at  it  a  moment.  We 
live  in  the  midst  of  a  material  world,  animate  and  inanimate,  and  have 
daily  converse,  so  to  speak,  with  material  forms  of  every  variety,  present- 
ing phenomena  of  the  highest  interest  and  of  endless  diversity.  And 
yet,  through  almost  all  the  period  of  childhood,  and  perhaps  we  may  say 
youth  also,  this  book  of  nature  is  in  the  school-room  very  nearly  a  sealed 
book.  The  very  process  of  education  shuts  in  the  pupil  from  this  broad 
contemplation  of  the  world  in  which  he  lives.  He  is  drilled  through 
spelling,  reading,  grammar,  &c.,  but  he  is  left  in  total  ignorance  of  the 
beautiful  flowers,  and  the  majestic  trees  outside  of  the  school-room.  How 
very  few  even  of  thoroughly  educated  adults,  know  the  processes  by 
which  a  plant  or  a  tree  grows!  And  the  same  can  be  said  of  other 
phenomena  of  nature. 

The  defect  which  I  have  pointed  out  runs  through  the  whole  of  educa- 
tion. We  can  see  it  even  in  the  prevalent  mode  of  teaching  the  natural 
sciences  themselves.  One  would  suppose  that  here  the  facts,  the  phe- 
nomena, would  command  the  chief  attention  of  the  teacher  and  the  stu- 
dent. But  it  is  very  commonly  not  so.  The  mere  technicalities  and  the 
classification  are  made  much  too  prominent.  Botany,  really  one  of  the 
most  interesting  of  all  branches  of  natural  science,  is  thus  ordinarily 
made  one  of  the  driest  of  studies.  To  teach  this  aright,  the  phenomena 
of  vegetation,  so  varied  and  so  beautiful,  should  constitute  the  chief  ma- 
terial of  instruction,  and  the  mere  classification  should  be  considered,  al- 
though necessary,  as  wholly  a  secondary  thing. 

The  great  facts  of  the  world,  both  of  mind  and  matter,  should  furnish 
really  the  material  for  education,  and  those  branches  that  are  ordinarily 
pursued  with  such  assiduity  should  be  considered  as  merely  subsidiary  to 
the  teaching  of  these  facts.  The  whole  order  of  education  must  be  re- 


PREFACE.  IX 


versed.  Instead  of  beginning  the  child's  education  with  learning  to  spell 
and  read,  the  object  should  be  to  make  him  an  observer  of  nature,  and 
the  spelling  and  reading  should  be  done  in  connection  with  this,  and  as 
subsidiary  to  it.  Things  and  not  words,  or  mere  signs,  should  from  the 
first,  constitute  the  substantial  part  of  instruction.  The  child  should  be 
made,  at  home,  in  the  school,  and  everywhere,  a  naturalist  in  the  largest 
sense  of  that  word.  We  should  aim  to  impart  to  him  a  spirit  in  con- 
sonance with  the  following  precept  of  Hugh  Miller,  the  famous  self- 
taught  geologist.  "  Learn  to  make  a  right  use  of  your  eyes ;  the  com- 
monest things  are  worth  looking  at — even  stones  and  weeds,  and  the 
most  familiar  animals." 

As  it  is  now,  no  one  becomes  a  naturalist  early  in  life,  except  in  spite 
of  the  tendencies  of  his  education.  The  study  of  nature  is  not  only  not 
encouraged,  but  is  absolutely  discouraged  in  our  educational  system.  If 
any  one,  like  Hugh  Miller,  by  the  force  of  a  taste  that  can  not  be  repress- 
ed by  the  training  of  the  school-room,  undertakes  to  make  a  "  right  use 
of  his  eyes,"  and  curiously  examines  "  stones  and  weeds,"  he  is  regard- 
ed by  the  world  of  spellers  and  readers  and  grammarians  and  cipherers, 
as  a  strange  genius.  But  he  is  pursuing  from  an  irresistible  internal 
force,  the  very  course  that  I  would  have  every  student,  even  from  his 
childhood,  encouraged  to  pursue,  in  a  measure  at  least,  by  the  external 
circumstances  of  his  education.  The  tendencies  of  his  training  should  be 
decidedly  in  this  direction. 

If  the  general  mode  of  education  were  changed  in  the  manner  indicated, 
education  would  have  much  less  of  the  character  of  mere  drudgery  than 
it  now  has.  Not  that  there  would  be  any  the  less  labor ;  but  the  labor 
would  be  made  lighter  by  the  interest  imparted  to  it — the  interest,  which 
always  results  from  the  study  of  facts  and  phenomena,  and  never  from  the 
learning  of  mere  words  and  technicalities  and  classifications.  I  would 
gladly  dwell  on  this  subject,  and  show  by  varied  illustrations  how  the 
mode  of  instruction  referred  to,  should  be  pursued,  and  especially  with 
younger  scholars $  but  the  limits  of  a  preface  will  not  allow  me  to  enter 
BO  large  a  field. 

The  change  which  I  have  pointed  out  can  not  be  effected  at  once.  It 
will  require  tune.  Confirmed  traditional  customs  are  to  be  done  away, 


PREFACE. 


the  habits  of  teachers  are  to  be  altered,  and  the  proper  books  are  to  * 
great  extent  to  be  yet  written,  especially  such  as  are  fitted  for  the  first 
years  of  education. 

If  the  study  of  nature  should  be  thus  made  prominent  in  education, 
human  physiology  would  be  considered  altogether  its  most  interesting  and 
important  branch,  and  for  several  reasons.  First :  there  is  no  where  to 
be  found  so  curious  a  collection  of  mechanisms,  or  so  interesting  and 
wonderful  a  series  of  processes,  as  in  the  human  body.  In  nothing  else 
in  the  wide  world  are  the  principles  of  so  many  departments  of  science 
so  extensively  and  perfectly  exemplified.  Life  works  here  its  most  com- 
plicated set  of  machinery.  Secondly :  the  singular  and  mysterious  con- 
nection of  the  immaterial  and  immortal  soul  with  the  material  and  perish- 
able body,  gives  intense  interest  to  this  study.  In  Physiology  we  do 
not  study  matter  alone,  or  spirit  alone,  but  both  matter  and  spirit  united, 
and  often  acting  together.  This  circumstance  distinguishes  this  from  all 
other  studies.  Thirdly :  it  is  our  own  frames,  moved  by  the  spirit  within 
us,  that  we  study.  The  subject  has  a  personal  interest  for  us,  that  is  not 
presented  by  most  studies,  and  by  none  in  so  large  a  degree  as  in  this. 
And  Fourthly :  the  study  is  of  great  importance,  because  a  judicious  and 
efficient  Hygiene  must  be  based  upon  a  knowledge  of  the  laws  of  physi- 
ology. We  cannot  know  how  to  keep  our  functions  in  the  condition  of 
health,  without  understanding  the  laws  that  regulate  them.  I  have  said 
but  little  in  this  book  in  regard  to  hygiene,  and  that  only  incidentally,  be- 
cause that  subject  would  require  of  itself  a  whole  volume  to  elucidate  it 
properly. 

I  have  not  thought  it  proper  to  indulge  to  any  great  extent  in  those  re- 
flections, which  the  contemplation  of  so  perfect  and  diversified  a  congeries 
of  mechanisms  as  are  presented  in  man  would  naturally  suggest,  in  regard 
to  the  skill  of  the  great  builder  of  the  universe.  Such  reflections  would 
extend  the  book  to  too  great  length.  Besides,  they  are  so  readily  sug- 
gested to  the  mind  of  both  teacher  and  scholar,  that  it  is  entirely  un- 
necessary for  the  author  to  dwell  on  them. 

I  have  treated  of  some  subjects,  on  which,  from  the  difficulty  of  un- 
derstanding them,  there  has  been  a  disposition  in  many  minds  to  go  be- 
*-ond  what  we  know,  and  indulge  in  unwarranted  speculation.  On  these 


PKEFACE.  XI 


points  I  have  taken  pains  to  draw  the  line  very  distinctly  between  what  is 
known,  and  what  is  supposed.  I  deem  it  to  bo  important  to  prevent  the 
minds  of  the  young  from  being  led  away  from  the  simple  truths  of 
science  by  ingenious  speculations  and  plausible  reasonings.  Let  me  not 
be  understood  to  decry  all  hypothesis.  I  only  object  to  the  mingling  of 
facts  and  suppositions  together  in  one  indiscriminate  mass,  as  is  often 
done.  The  disposition  to  do  this,  which  is  more  common  than  is  generally 
supposed,  exerts  so  injurious  an  influence  upon  the  habile  of  the  mind, 
and  so  confuses  its  views  of  truth,  that  we  ought  to  look  upon  it  as  one  of 
the  most  serious  evils  to  be  guarded  against  in  education.  It  is  really 
one  of  the  most  prominent  obstacles  to  the  progress  of  truth  on  all  sub- 
jects, both  in  individual  minds,  and  in  the  minds  of  the  community  at 
large.  This  disposition,  so  apt  to  be  fostered  in  the  enthusiastic  mind  of 
youth,  by  ingenious  but  dreamy  speculations,  should  be  corrected  at  tho 
outset,  and  the  mind  should  in  its  forming  stage,  ba  habituated  to  the  dis- 
crimination between  the  proved,  the  true,  and  that  which  rests  on  pre- 
sumptive, perhaps  merely  plausible  evidence.  This  discrimination  should 
therefore  be  exemplified  in  books  designed  for  instruction,  and  this  I  have 
attempted  in  the  present  volume. 

I  have  divided  the  book  into  Three  Parts.  The  First,  which  I  have 
made  as  short  as  possible,  is  merely  preliminary  to  the  consideration  of 
the  particular  subject  of  the  book.  In  the  Second  Part,  I  present  the 
human  structure,  simply  as  a  structure,  and  show  how  it  is  constructed 
and  kept  in  repair.  In  the  Third  Part,  I  treat  of  all  those  subjects  which 
relate  to  the  uses  for  which  the  structure  is  designed.  This  natural 
division  of  the  whole  subject,  not  only  presents  it  to  the  mind  of  the 
student  in  an  interesting  point  of  view,  but  secures  that  natural  grada- 
tion in  its  development,  which  I  have  spoken  of  as  being  necessary  to  a 
clear  understanding  of  its  deeper  and  more  intricate  portions. 


NOTE. 


SINCE  the  book  was  first  published,  the  Author 
has,  in  obedience  to  the  requests  of  many  Teachers, 
added  a  chapter  on  HYGIENE,  and  also  an  APPENDIX 
containing  questions.  A  full  INDEX  is  also  subjoined. 


PHYSIOLOGY 


PART  FIRST, 

CONTAINING, 

CHAPTER  I ORGANIZED  AND  UNORGANIZED  SUBSTANCES.    CHAPTER  II — Tmt  DisnNcnorr 

BETWEEN  ANIMALS  AND  PLANTS.    CHAPTER  III.— MAJT  IN  HIS  RELATIONS  TO  TIM  Tmir* 
KINGDOMS  or  NATURE. 


CHAPTER  I. 

ORGANIZED  AND  UNORGANEED  SUBSTANCES. 

1.  THE  crystal  and  the  plant  are  both  wonderful  growths. 
As  you  look  at  them,  you  think  -of  the  crystal  as  having  been 
formed,  and  of  the  plant  as  having  grown.     But  in  one  sense 
they  have  both  grown  to  be  what  they  are.     The  crystal  was 
once  a  minute  nucleus,  and  the  plant  was  once  a  little  germ. 

2.  In  one  respect  they  are  alike  in  their  growth — both  have 
increased  from  particles  taken  from  things  around  them.     But 
the  processes  by  which  this  is  done  are  different  in  the  two 
cases.     The  crystal  has  increased  or  grown  by  layer  after  layer 
of  particles.     There  are  no  spaces  or  passages  by  which  parti- 
cles of  matter  can  be  introduced  inside  of  it.     Any  part  of  it, 
when  once  formed,  is  not  altered.     It  can  receive  additions 
upon  the  outside  alone.     But  it  is  not  so  with  the  plant.     This 
enlarges  by  particles  which  are  introduced  into  passages  and 
interstices.     It  grows,  as  it  is  expressed,  by  absorption  or  by  in- 
tussusception. 

3.  How,  now,  is  this  absorption  effected?     It  is  done  by  cer- 
tain vessels  or  organs,  constructed  in  the  root  of  the  plant  for 
this  purpose.     These  take  up  or  absorb  fluid  matter  from  the 
earth.    There  are  other  organs  which  circulate  this  fluid  through 
all  the  plant ;  and  others  still  which  use  it  for  the  purpose  of 
growth  or  formation.     There  are  no  such  organs  in  the  crystal, 
for  it  has  no  inner  growth.     The  plant  is  therefore  said  to  be 
an  organized  substance  or  being,  and  the  crystal  is  an  unor- 
ganized substance.     And  so  we  speak  of  the  organic  structure, 
or  the  organization  of  plants. 


14  HUMAN  PHYSIOLOGY. 


Organized  beings.    Mechanical,  chemical,  and  vital  principles. 


4.  These  organs,  which  thus  absorb,  and  circulate,  and  con- 
struct, do  not  act  simply  on  mechanical  principles.     The  plant 
is  not  merely  soaked  with  fluid,  which  the  heat  of  the  sun  may 
expel,  as  it  does  water  from  a  porous  mineral  substance.    These 
organs  are  active  agents,  and  they  perform  their  duty  with  a 
force,  and  after  a  manner,  for  which  no  mechanical  principles 
can  account.     No  mechanical  powers  could  alone  supply  the 
leaves  of  the  mighty  tree  of  the  forest  with  sap  from  its  deep 
roots ;  much  less  could  they  form  these  leaves. 

5.  Neither  do  these  organs  act  simply  on  chemical  princi- 
ples.    While  man,  through  the  agency  of  chemistry,  can  form 
some  of  the  crystals  which  are  found  in  nature,  he  can  not  by 
any  arrangement  of  constituents  make  a  plant,  a  flower,  or  a 
leaf.     And  the  plant,  left  alone  to  the  action  of  chemical  prin- 
ciples, wilts ;  and  at  length  ceases  to  be  a  plant,  and  becomes 
common  unorganized  matter. 

6.  Mechanical  and  chemical  principles,  it  is  true,  are  both 
employed  to  some  extent  in  the  growth  of  plants ;  but  they  are 
under  the  control  of  other  principles,  which  we  term  vital.    And 
so  we  speak  of  the  plant  not  only  as  an  organized  substance, 
but  as  a  living  being. 

7.  What  I  have  said  of  plants,  in  distinction  from  minerals, 
may  also  be  said  of  animals.     They  are  also  organized  living 
beings,  and  they  have  generally  a  more  complex  organization 
than  plants,  as  you  will  see  as  I  proceed. 

8.  The  whole  material  world,  then,  that  we  see  around  us, 
we  divide  into  two  parts — the  unorganized  and  lifeless,  and  the 
organized  and  living.     The  distinctions  thus  pointed  out  be- 
tween organized   and  unorganized   matter   are  essential  and 
fundamental.    But  let  us  look  at  some  other  distinctions,  which 
either  arise  from  these  or  accompany  them. 

9.  One  distinction  is  this.     All  the  parts  of  the  mineral  are 
independent  of  each  other,  while  it  is  otherwise  with  the  plant 
or  the  animal.    Accordingly,  we  examine  the  properties  of  min- 
erals in  a  different  way  from  those  of  plants  and  animals.     The 
chemist  can  ascertain  all  the  properties  of  a  crystal  or  a  rock, 
if  you  give  him  but  a  small  piece  of  it.     But  the  botanist  can 
not  ascertain  all  the  properties  of  a  plant  by  looking  at  some 
one  part  of  it.     If  he  examine  the  flower,  this  gives  him  no 
knowledge  of  the  root.     In  order  to  know  all  about  the  plant, 
he  must  examine  every  part  by  itself,  and  then  look  at  it  in  its 
relations  to  the  other  parts.     The  same  can  be  said  of  tha 
physiologist,  in  his  investigation  of  the  properties  of  animals. 


ORGANIZED  AND   UNORGANIZED  SUBSTANCES.       15 

Assimilation  in  organized  substances. 

10.  As  the  crystal  is  forming  by  layer  after  layer  of  particles, 
no  change  is  effected  in  these  particles  as  they  are  becoming 
arranged  in  the  layers.     But  in  the  case  of  the  living  organ- 
ized being,  a  change  is  produced  in  the  particles  which  are 
taken  up  by  the  absorbents.     And  the  change,  ordinarily,  is 
both  a  gradual  and  a  complex  one.     In  the  plant,  a  change  is 
produced  in  the  particles  in  the  very  act  of  absorption;  but 
this  change  is  only  the  beginning  of  a  process  which  is  after- 
wards perfected.     The  sap  is  not  thoroughly  fitted  for  nutrition 
when  it  first  begins  to  circulate.     It  is  carried  up  through  the 
vessels  of  the  trunk  or  stalk  to  the  leaves.     There  the  last  step 
of  the  process  is  taken,  and  the  sap  is  now  ready  to  be  used  in 
the  growth  of  the  plant  or  tree.     So,  also,  in  the  animal,  the 
nutritious  part  of  the  food,  taken  up  by  the  absorbents  in  the 
digestive  organs,  is  first  acted  upon  by  certain  little  glands, 
through  which  it  passes,  is  then  poured  into  the  circulation,  to 
be  mingled  with  the  blood,  and  is  carried  with  the  blood  to  the 
lungs,  to  be  exposed  to  the  air ;  and  thus  it  is  fitted  for  the  nu- 
trition or  growth  of  the  body.    This  process,  which  is  thus  car- 
ried on  in  the  plant  and  in  the  animal,  is  very  properly  called 
assimilation.     For  the  particles  that  are  taken  up  by  the  ab- 
sorbents in  the  root  of  the  plant  are,  by  this  process,  made  like 
to  the  plant ;  and  the  particles  taken  up  by  the  absorbents  in 
the  stomach  *  are  made  like  to  the  animal.    So  obvious  is  this, 
in  the  case  of  the  animal,  that  some  French  physiologist  speaks 
of  the  blood  as  chair  coulante,  or  running  flesh. 

11.  Another  prominent  distinction  between  organized  and 
unorganized  substances  is  in  relation  to  permanency.    Constant 
change  appears  in  all  organized  bodies ;  while  permanency  is 
written  upon  all  substances  which  are  unorganized.     In  organ- 
ized beings,  continual  change  is  going  on  at  every  point.     It  is 
a  condition  of  their  being.     This  is  true,  not  only  of  the  de- 
cline of  a  plant  or  animal,  but  even  of  its  growth.     For,  in  its 
growth,  as  the  parts  enlarge  internally  as  well  as  externally, 
they  change  not  only  the  arrangement  of  the  particles,  but,  to 
a  great  extent,  they  change  the  particles  themselves.     It  is 


*  The  word  stomach  requires  some  little  explanation,  as  it  is  used  in  physiology  in  two 
senses — in  a  limited  sense,  and  also  in  an  extended  one.  It  is  used  in  its  limited  sense,  as 
referring  to  the  cavity  at  the  beginning  of  the  alimentary  cann/,  as  it  is  termed;  this  lat- 
ter term  being  applied  to  the  series  of  cavities,  the  stomach  and  the  small  and  large,  intes- 
tines, which  are  fuuod  in  the  digestive  apparatus  in  the  higher  orders  of  animals.  In 
comparisons,  however,  between  these  animals  and  those  which  have  a  more  simple  digest- 
ive apparatus,  the  word  stomach  is  used  in  a  more  extended  sense,  as  being  synonymou* 
with  the  term  alimentary  canal.  It  is  used  in  this  sense,  also,  when,  as  in  the  present 
oase,  it  is  referred  to  in  a  comparison  between  animals  and  vegetables. 


16  HUMAN  PHYSIOLOGY. 

Organized  substances  changing.    Unorganized  permanent. 

true,  as  well  of  the  towering  tree  as  of  the  tiny  plant,  that 
these  changes  have  been  going  on  during  all  its  growth ;  so 
that,  at  its  maturity,  it  is,  both  in  relation  to  the  arrangement 
of  its  particles,  and  in  relation  to  the  particles  themselves,  a 
very  different  thing  from  what  it  was  when  it  pushed  its  germ 
up  through  the  ground,  or  even  when  it  was  but  a  small  tree. 
Not  only  has  it  received  into  its  interstices  and  passages  new 
particles,  but  it  has  thrown  off  from  the  pores  of  its  leaves, 
those  outlets  for  the  refuse  of  plants,  vast  quantities  of  parti- 
cles which  are  no  longer  of  use  in  its  structure.  So,  in  all 
animals,  the  same  internal  changes  are  going  on,  and  to  a 
much  greater  extent ;  because,  from  the  activity  of  their  na- 
ture, there  is  more  of  wear  and  tear,  and,  therefore,  more  of 
refuse  matter  to  be  disposed  of.  As  you  will  see  in  another 
part  of  this  book,  the  human  body,  that  most  complicated  of 
organized  beings,  undergoes  these  changes  very  largely. 

12.  It  is  not  thus  with  unorganized  substances.     The  crys- 
tal, so  fast  as  it  is  formed,  becomes  permanent.     No  changes 
occur  within  it.     In  itself,  it  is  unchangeable.     It  can  not 
change  its  own  particles,  as  the  plant  or  the  animal  does.     It 
can  be  changed  only  by  external  addition,  or  by  external  dimi- 
nution, through  the  influence  of  agents  acting  upon  its  surface. 

13.  With  the  constant  changes  going  on  in  organic  nature, 
there  is  constant  succession.    Plants  and  animals  produce  other 
plants  and  animals,  and  themselves  die,  making  room  for  their 
successors.     But  the  crystal  does  not  form  other  crystals,  and 
then  crumble  into  dust.     In  itself,  it  is  both  unchangeable  and 
unproductive. 

14.  This  distinction  between  organized  and  unorganized  sub- 
stances, in  relation  to  change  and  succession,  meets  the  eye 
everywhere.     The  mountains,  the  rocks,  and  even  the  stones 
under  our  feet,  remain  the  same  year  after  year,  while  all  vege- 
table and  animal  life  is  ever  changing  its  forms  and  manifesta- 
tions.    There  are  the  changes  of  growth,  and  the  changes  of 
decay  and  death,  all  around  and  within  us;   and  they  are 
strangely   mingled   together.      There   is   death   even   in   the 
changes  of  life,  as  the  waste  particles  are  taken  away,  and  are 
replaced  by  the  new ;  and  life  springs  out  of  the  very  bosom 
of  death,  as  from  decayed  nature  new  forms  of  vigor  and 
beauty  arise.     The  mountains  stand  as  they  have  stood,  as  the 
passing  generations  have  looked  upon  them,  while  the  continual 
changes  of  vegetation  have  been  going  on  upon  and  around 
them.     The  seasons  crown  their  battlements  with  the  emblemi 


ORGANIZED  AND   UNORGANIZED  SUBSTANCES.       17 
Different  forms  of  organized  and  unorganized  substances. 

of  their  ever-returning  mutations  of  life,  decay,  and  death; 
and  even  the  mighty  trees,  that  have  shed  their  leaves  from 
year  to  year,  in  obedience  to  the  great  law  of  change,  but  have 
themselves  stood,  at  length  bow  their  heads  to  the  same  law, 
and  give  place  to  other  lords  of  the  forest.  From  the  "  ever- 
lasting hills,"  which  thus  remain  the  same,  though  change  is 
ever  about  and  upon  them,  man  gets  the  unchangeable  and 
imperishable  rock  to  construct  his  habitation,  while  he  himself 
is  changeable  and  perishable — the  creature  of  a  day,  whose 
life  is  as  a  vapor.  He  wears  the  precious  stones,  and  traffics 
in  the  golden  ores,  which  have  existed  from  the  creation  of  the 
world,  through  all  the  changing  and  dying  generations,  and 
passes  away,  leaving  them  to  others  as  changeable  and  perish- 
able as  himself. 

15.  Another  distinction  between  organized  and  unorganized 
substances  relates  to  the  forms  which  they  assume.     There  is 
regularity  in  both,  but  it  is  different  in  each.     Unorganized 
matter  is  disposed  to  arrange  its  particles  in  straight  lines,  and 
with  angles  mathematically  exact.    You  see  this  in  the  beautiful 
crystal ;  and  you  also  see  it,  less  definitely,  but  magnificently, 
displayed  in  the  regular  battlements  and  columns  of  rocks  and 
mountains.     The  tendency  is  to  regularity ;  and  irregularity  is 
the  result  of  interfering  circumstances.     A  similar  disposition 
to  regularity  is  manifest   in  organized  substances,  but  in  a 
different  manner.    It  is  disposed  to  curved,  rather  than  straight 
lines,  and  seldom  makes  lines  or  angles  with  mathematical  ex- 
actness.    We  see  this  .law  of  regularity  exemplified  both  in 
animal  and  vegetable  life.    The  leaf,  for  example,  has  the  same 
general  shape,  that  is,  the  same  general  arrangement  of  par- 
ticles, when  it  attains  its  full  size,  that  it  had  when  it  was 
small ;  and  the  same  can  be  said  of  the  arm  of  the  man,  com- 
pared with  his  arm  when  a  child.     Illustrations  might  be  cited 
to  any  extent,  but  these  are  sufficient. 

16.  While  the  law  of  regularity  is  not  commonly  as  exact 
in  organized  substances  as  it  is  in  the  unorganized,  it  is  quite 
as  authoritative.     While  it  does  not  ordinarily  observe  the  per- 
fectly straight  lines  and  the  unvarying  angles  which  we  always 
find  in  the  crystal,  the  general  plan  and  contour  are  very  strictly 
preserved  amid  all  the  changes  of  animal  and  vegetable  life. 
And,  in  some  cases,  the  same  mathematical  exactness  that  we 
find  in  the  mineral  world  is  found  in   organized  beings.     I 
know  not  that  this  is  ever  true  of  straight  lines  and  angles ; 
but  it  is  often  true  of  curved  lines.     There  are  many  very 

2* 


18  HUMAN  PHYSIOLOGY. 

Regularity  in  form — in  some  cases  wonderful. 

beautiful  examples  in  the  vegetable  world.  I  will  give  but  a 
single  one.  If  you  look  at  the  common 'white  daisy,  before  tho 
hundreds  of  little  buds  in  its  bosom  have  opened  into  tiny 
flowers,  you  will  see  them  arranged  with  great  exactness  in 
crossing  curved  lines,  such  as  you  often  see  on  the  back  of 
a  watch  case.  A  similar  arrangement  you  will  find  in  many 
flowers. 

17.  This  regularity  is  more  wonderful   in   organized  sub- 
stances than  in  the  unorganized,  because  it  rules  in  them  in  the 
midst  of  constant  change.     In  the  case  of  the  crystal,  as  there 
are  no  internal  changes  in  it,  and  as  each  layer  of  it,  when 
formed,  is  permanent,  regularity  is  comparatively,  so  to  speak, 
easily  secured.     But  in  the  case  of  the  leaf,  as  it  is  growing  to 
its  full  size,  and  of  the  arm,  as  it  grows  from  infancy  to  be 
the  stalwart  arm  of  manhood,  continual  change  is  going  on  at 
every  point ;  and  regularity  here  is  obviously  a  more  difficult 
achievement. 

18.  This  regularity  appears  still  more  wonderful,  when  we 
look  at  the  infinite  variety  of  forms  in  organized  matter,  in 
both  the  vegetable  and  the  animal  world.     In  all  these  forms, 
each  part  of  every  animal  and  of  every  plant  maintains  its 
own  peculiar  plan  and  contour.     Take,  for  example,  the  leaf  in 
its  endless  varieties.     How  definitely  does  each  variety  preserve 
its  individual  character,  and  how  easily  is  it  distinguished  from 
every  other  variety !     The  same  can  be  said  of  every  part  of 
every  organized  being. 

19.  Another  circumstance  still  must  be  mentioned,  as  adding 
to  the  wonderfulness  of  this  regularity.     It  has  been  scrupu- 
lously maintained,  through  all  the  changes  of  the  world  from 
its  creation,  when  God  pronounced  the  works  of  his  hands  to 
be  "very  good."     The  leaf  of  every  tree,  for  example,  is  like 
the  leaf  of  its  ancestral  trees  back  to  that  time ;  and  so  it  will 
be  in  all  its  successors  to  the  end  of  the  world.     "  The  trees  of 
the  garden,"  which  delighted  the  eyes  of  our  first  parents,  and 
refreshed  them  with  their  shade  in  their  innocence,  and  amid 
which  they  hid  themselves  after  their  sin  from  the  presence  of 
their  Maker,  undoubtedly  had  the  same  characteristic  shapes, 
and  the  same  leaves  and  flowers  which  their  successors  present 
to  our  eyes. 

20.  Again,  it  is  interesting  to  notice  that,  in  the  midst  of 
this  regularity,  so  strictly  maintained  in  each  specific  form  from 
age  to  age,  there  is  a  measure  of  irregularity  allowed.     While 
each  kind  of  tree,  for  example,  has  specific  characteristics  in 


ORGANIZED  AND   UNORGANIZED  SUBSTANCES.       19 

Variety  of  form ;  yet  regularity  preserved.     Size. 

the  arrangements  of  branches  and  other  parts,  and  in  the 
shapes  of  "its  leaves,  no  two  trees  of  the  same  kind  are  exactly 
alike,  and  there  is  always  much  variety  in  the  leaves  of  the 
same  kind.  The  wonder  is,  that  so  much  latitude  is  allowed 
in  this  respect,  and  yet  the  specific  characteristics  of  each  kind 
are  so  thoroughly  preserved.  We  can  readily  see  that  if  a 
pattern,  definite  in  all  its  details,  were  to  be  copied  exactly  in 
each  kind  of  vegetable  and  animal  form,  the  distinctions  between 
them  could  be  more  easily  preserved.  But  Omnipotence  is 
able  to  combine  a  wide  latitude  and  variety  of  form  in  each 
kind,  with  a  strict  and  uniform  preservation  of  its  characteristic 
contour  and  arrangement.  We  have  a  striking  exemplification 
of  the  above  remarks  in  the  variety  of  the  human  countenance. 
While  the  face  of  man  is  so  entirely  different  from  the  face  of 
every  other  animal,  at  the  same  time,  among  the  hundreds  of 
millions  of  the  human  family,  how  uncommon  it  is  to  find  two 
faces  that  are  very  nearly  alike. 

21.  In  the  animal  world,  we  see  remarkable  examples  of  the 
preservation  of  regularity  of  form  in  the  exact  correspondence 
which  exists  so  commonly  between  the  two  halves  of  the  body. 
For  example,  the  brain  has  two  halves,  which  are  precisely  alike, 
and  the  same  is  true  of  the  nerves  which  are  distributed  from 
it.     And  so  of  other  parts.     But,  mingled  with  this  symmetri- 
cal arrangement  of  parts,  there  are  other  parts  which  are  irreg- 
ular in  their  shape.     This  is  the  case  with  the  stomach,  the 
heart,  the  liver,  <fec.     There  are  some  animals  which  are  alto- 
gether destitute  of  this    arrangement  of  two  similar  halves  of 
the  body.     The  oyster  is  a  familiar  example.     The  shell  of  this 
animal  is  strikingly  in  contrast,  in  this  respect,  with  the  shells 
of  some  other  of  the  bivalve  tribe,  as,  for  instance,  the  common 
clam. 

22.  There  is  a  distinction  between  organized  and  unorganized 
substances,  in  regard  to  size,  which  must  not  pass  unnoticed  in 
this  connection.     The  size  of  unorganized  bodies  has  no  fixed 
limit.     A  crystal  or  a  rock  may  grow  to  any  imaginable  size, 
if  the  particles  forming  'it  are  sufficiently  abundant.     But  or- 
ganized bodies  have  limits  fixed  to  their  growth.     There  is,  it 
is  true,  more  or  less  latitude  to  these  limits ;  but  they  are  so 
well  defined  in  the  case  of  most  vegetables  and  animals,  that 
when  growth  reaches  much  beyond  or  below  the  limit,  it  is 
recognized  as  a  remarkable  fact.     Gigantic  and  dwarfish  vari- 
ties  are  rare  exceptions  to  the  general  rule. 

23.  The  last  distinction,  between  organized  and  unorganized 


20  HUMAN  PHYSIOLOGY. 

Difference  between  organized  and  unorganized  in  structure  and  elements. 

substances,  which  I  shall  mention  relates  to  their  structure. 
While  unorganized  substances  are  made  of  one  form  of  matter, 
either  solid  or  liquid,  or  gaseous,  organized  bodies  are  made  of 
a  mixture  of  fluids  and  solids.  They  are  therefore  more  or  less 
soft  and  flexible;  while  the  solid,  unorganized  substances  are 
hard  and  brittle.  There  is  a  still  further  difference  in  struc- 
ture. Organized  substances  are  much  more  compound  than 
the  unorganized.  Most  of  the  unorganized  substances  are 
composed  of  only  two  or  three  elements.  Thus,  air  is  com- 
posed of  oxygen  and  nitrogen,  water  of  oxygen  and  hydro- 
gen ;  and  most  of  the  mineral  salts  are  composed  of  three 
elements — as,  for  example,  carbonate  of  lime,  or  chalk,  which 
is  composed  of  oxygen,  carbon,  and  calcium,  the  mineral  base 
of  lime.  But  organized  substances  are  composed  of  at  least 
three  or  four  elements,  and  sometimes  more.  The  four  princi- 
pal elements  in  the  composition  of  organized  bodies  are,  oxygen, 
nitrogen,  hydrogen,  and  carbon.  But  there  are  other  elements 
introduced  for  special  purposes.  Thus,  carbonate  of  lime  (a 
combination  of  calcium  with  two  of  the  common  elements, 
carbon  and  oxygen,)  is  diffused  very  generally  throughout  the 
textures  of  plants,  giving  them  firmness  and  strength.  In  the 
grass  tribe,  silex  is  deposited  under  the  surface,  producing  the 
necessary  combination  of  strength  and  lightness,  a  very  small 
quantity  of  the  silex  answering  the  purpose.  In  animals  of 
the  higher  orders,  phosphate  and  carbonate  of  lime  compose  in 
part  the  framework  of  the  body.  We  find  iron,  too,  in  the 
blood.  Of  the  fifty-four  elementary  substances  discovered  in 
mineral  bodies,  only  eighteen  or  nineteen  have  been  found  in 
plants  and  animals,  and  some  of  these  in  very  small  amounts. 
The  essential  components  of  living  substances  are  the  four  non- 
metallic  elements  mentioned  above — oxygen,  hydrogen,  nitro- 
gen, and  carbon;  while  the  bulk  of  the  inorganic  world  is 
composed  of  the  metals  and  their  compounds,  viz.,  the  alkalies 
and  the  earths.  And  it  is  interesting  to  observe  that,  of  the 
four  elements  which  compose  the  bulk  of  the  animal  and  vege- 
table world,  both  the  fluids  and  the  Solids,  three  are  gaseous, 
while  but  one,  carbon,  is  a  solid  substance. 


DISTINCTIONS  BETWEEN  ANIMALS  AND  PLANTS.      21 
Locomotion.    Stomach  and  other  central  organs. 

CHAPTER  II. 

THE  DISTINCTIONS  BETWEEN  ANBTALS  AND  PLANTS. 

24.  HAVING  pointed  out  in  the  first  chapter  the  distinctions 
between  organized  and  unorganized  substances,  I  now  proceed 
to  consider  the  distinctions  between  the  two  classes  of  organ- 
ized beings — animals  and  vegetables.     I  shall  first  notice  those 
differences  which  are  obvious  when  we  look  at  the  great  major- 
ity of  animals  and  vegetables ;  and  shall  then  point  out  those 
which  are  essential,  in  order  that  we  may  have  a  clearer  view  of 
those  exceptional  cases,  in  regard  to  which  it  is  somewhat 
difficult  to  decide  to  which  of  the  two  kingdoms  they  belong. 

25.  One  of  the  most  obvious  distinctions  is  in  relation  to 
locomotion.     The  plant  remains  in  one  place ;  while  the  animal 
moves  about,  in  the  air,  or  in  the  water,  or  upon  the  surface  of 
the  earth.     And  the  structures  of  the  animal  and  the  plant  of 
course  differ,  so  as  to  accommodate  these  two  very  different 
modes  of  existence.    I  will  particularize.    As  the  animal  moves 
from  place  to  place,  it  must,  for  this  reason,  if  for  no  other, 
have  an  apparatus  of  nourishment  and  growth  different  from 
that  of  the  plant.     The  plant,  by  means  of  its  absorbents  in 
the  roots,  takes  up  from  the  earth,  in  the  form  of  sap,  its  nutri- 
tion, or  food,  as  it  may  very  properly  be  called.     The  moving 
about  of  the  animal  would  in  itself  forbid  its  deriving  its  food 
directly  from  the  earth,  even  if  the  earth  contained  the  proper 
materials   for    its    nourishment.      Another   contrivance   must 
therefore  be  resorted  to,  in  order  to  effect  nutrition  in  its  case. 
So  a  cavity  is  provided  in  its  body,  called  a  stomach,  into 
which  nutritious  substances  can  be  introduced.     And  this  cav- 
ity is  lined  with  absorbents,  which  there  do  for  the  animal 
just  what  the  absorbents  in  the  roots  of  the  plant  do  for  the 
plant. 

26.  Besides  the  stomach,  there  are  other  great  central  or- 
gans which  are  peculiar  to  most  animals,  in  distinction  from 
vegetables — as  the  heart,  the  liver,  the  lungs,  <kc.     In  the 
plant,  there  are  no  such  central  organs  upon  which  the  whole 
plant  depends.    Branches  and  roots  may  be  cut  off  extensively, 
and  even  a  large  portion  of  the  stem  or  trunk  may  be  des- 
troyed ;  and  yet  what  remains  of  the  plant  may  still  live.     And 


22  HUMAN  PHYSIOLOGY. 


Feeling.     Motion.     Sensitive  plant  and  catch-fly. 


even  more  than  this.  A  small  portion  of  it  may  be  made  to 
take  root  and  live  by  itself.  It  is  not  so  with  most  animals. 
Mutilation  can  not  be  carried  far  without  injuring  some  large 
organ  which  is  essential  to  the  life  of  the  whole ;  and  no  part 
taken  from  its  extremities  can  be  made  in  any  way  to  live  by 
itself. 

27.  Another  obvious  distinction  is  this.     Animals  are  sen- 
tient and  spontaneously-moving  beings,  while  vegetables  are  not. 
The  animal  feels  the  action  of  agents  upon  it,  and  this  it  can 
not  do  without  consciousness  and  thought.   The  evidences  of  the 
existence  of  consciousness  and  thought,  and  the  consequent  spon- 
taneous motion,  are  very  slight  in  some  animals.   Still,  there  is  no 
doubt  of  their  existence  in  these  cases.    We  see  these  evidences 
plainly  in  the  great  majority  of  animals ;  and  we  infer,  very 
properly,  the  existence  of  sensation  and  thought  in  those  excep- 
tional cases,  where  the  evidences  are  doubtful  or  absent,  as  we 
find  in  them  other  marks  of  animal  in  distinction  from  vege- 
table life. 

28.  The  distinctions  which  I  have  mentioned  are  those  which 
we  see  generally  existing.    Let  us  see  how  far  they  are  essential 
and  universal. 

29.  The  distinction  in  regard  to  locomotion,  if  we  look  at 
the  animal  as  a  whole,  has  its  exceptions.     There  are  some 
animals  that  are  entirely  confined  to  one  spot  during  all  their 
existence,  as  the  coral  animal  and  the  sponge.     But,  while 
some  animals  are  thus  confined,  they  have  the  power  of  spon- 
taneous motion  in  some  of  their  parts,  which  is  exercised  for 
the  purpose  of  obtaining  food,  and,  in  some  cases,  for  the 
avoidance  of  danger.    This  power  is  not  possessed  by  any  plant. 
Some  few  plants,  as  the  sensitive  plant  and  the  Venus  catch-fly, 
(dionaea  muscipula,)  exhibit  a  property  which  resembles  it,  but 
it  is  essentially  a  different  thing.     In  these  cases,  the  influence 
of  the  stimulus  that  excites  the  motion  is  communicated  from 
particle  to  particle,  from  the  point  where  the  stimulus  is  ap- 
plied; and  the  motion  is  only  in  one  direction,  and  not  in 
various  directions,  as  is  the  case  with  spontaneous  animal  mo- 
tions.   This  can  be  very  readily  seen,  if  we  compare  the  motion 
of  the  sensitive  plant  or  the  catch-fly  with  those  of  the  little  fresh- 
water polype,  called  the  Hydra.     This  animal,  of  which  I  give 
you  here  an  enlarged  representation,  and  also  a  representation 
of  its  natural  size,  is  found  in  ponds.     It  attaches  itself  to  any 
floating  object — a  stick  or  straw,  as  seen  in  the  Figure — by  a 
kind  of  sucker.    Thus  supporting  itself,  it  stretches  out  its  long 


DISTINCTIONS  BETWEEN  ANIMALS  AND  PLANTS.      23 


Digestive  cavity.    Nervous  system.    None  in  plants. 


FIG.  1. 


HYDRA. 


arms,  to  take  for  its  food  any 
minute  worm  or  insect  which 
may  float  within  their  reach. 
When  it  catches  one,  it  directs 
it  to  the  mouth,  a,  which  opens 
into  the  stomach  or  general  cav- 
ity. Now,  in  doing  all  this, 
there  is  a  variety,  a  compound 
character  in  the  motion,  which 
is  in  plain  contrast  with  the 
simple  motion  of  the  leaves  of 
the  catch-fly  and  the  sensitive 
plant. 

30.  The  distinction,  in  rela- 
tion to  a  digestive  cavity,  can 
not  be  made  out  in  the  case  of 
some  of  the  lower  animals.  And, 
if  it  could  be,  it  is  not  an  essen- 
tial   distinction.      For   it   only 
relates  to  a  mere  difference  of 
arrangement  in  the  absorbents 

that  take  up  the  nutritious  substance  in  the  two  cases.  The 
absorbents  in  the  stomach  of  the  animal,  as  before  remarked, 
perform  the  same  office  that  the  absorbents  do  in  the  root  of 
the  plant.  They  only  do  it  in  a  different  place,  and  after  a 
different  manner.  The  same  remarks,  substantially,  can  be 
made  in  regard  to  the  other  large  central  organs  which  are 
found  in  most  animals. 

31.  The  last  of  the  distinctions,  which  I  mentioned  as  being 
commonly  observed,  is  really  the  essential  distinction  between 
plants  and  animals.     I  mean  the  capacity  for  sensation  and 
spontaneous  motion,  which  exists  only  in  the  animal.     There 
is  nothing  truly  analogous  to  this  in  the  plant.     And  we,  ac- 
cordingly, find  a  peculiar  structure  in  animals,  devoted  to  these 
functions,  and  others  connected  with  them.     This  structure  is 
the  nervous  system.     No  trace  of  such  a  structure  has  ever 
been  discovered  in  any  plant.     If  there  were  any  true  analogy 
between  animal  motion  and  the  motions  of  the  sensitive  plant 
and  the  catch-fly,  we  should  be  able  to  find  in  them  traces  of  ner- 
vous structure ;  for  the  structure  of  these  plants  is  so  plainly 
developed,  that  its  constituent  parts  are  easily  distinguished. 

32.  The  nervous  system  is  evidently  not  essential  to  nutri- 
tion, for  this  is  as  well  effected  in  the  plant  as  in  the  animal. 


24.  HUMAN  PHYSIOLOGY. 

Thought  and  will.    Instinctive  and  automatic  motions. 

This  is  accomplished  in  both  in  substantially  the  same  way. 
The  means  by  which  it  is  done,  and  its  arrangements  are  modi- 
fied, as  you  have  seen,  in  the  two  cases,  to  suit  the  differing 
circumstances.  The  nervous  system,  observe,  then,  is,  for  par- 
ticular purposes,  superadded  in  the  animal  to  what  ?.s  common 
both  to  the  animal  and  the  plant,  and  so  constitutes  the  essen- 
tial difference  between  them.  And  so,  all  the  functions  relating 
to  nutrition,  which  are  of  course  common  to  plants  and  animals, 
are  called  functions  of  organic  life.  But  the  functions  which 
are  performed  by  the  system  superadded  in  the  animal,  the 
chief  of  which  are  sensation  and  spontaneous  motion,  are 
termed  functions  of  animal  life.  These  are  sometimes  also 
called  functions  of  relation,  from  the  especial  connection  which 
they  form  between  the  animal  and  all  that  is  around  him. 

33.  These  animal  functions,  sensation  and  spontaneous  mo- 
tion, imply  thought  and  will.     The  order  of  action  is  this: 
sensation — thought  in  regard  to  it — action  of  the  will  in  con- 
sequence of  thought — then,  from  this  action,  an  impression 
carried  through  nerves  to  organs  termed  muscles — motion  in 
them  from   their   contraction.      This   order,  however,  is  not 
always  observed.      The  first   link,  sensation,  may  be  absent. 
Thought,  without  any  preceding  sensation,  may  prompt  the 
will,  and  spontaneous  motion  results.     The  action  of  the  will, 
too,  may  be  left  out,  or  may  be  in  opposition.     Thus,  emotions 
may  produce  action  of  the  muscles,  the  will  not  concurring, 
and  perhaps  opposing ;  as  when  we  laugh  at  what  is  ridiculous, 
or  weep  at  what  is  sad,  in  spite  of  restraining  efforts  dictated 
by  the  will. 

34.  There  are  also  instinctive  motions,  and  motions  which 
are  termed  automatic,  with  which  the  will  has  no  direct  con- 
nection.    And  the  connection  of  sensation  with  them  is,  in 
some  cases  at  least,  doubtful.     The  action  of  the  muscles,  in 
swallowing,  breathing,  &c.,  and  the  action  of  that  compound 
muscle,  the  heart,  are  examples  of  motions  more  or  less  dis- 
connected from  the  will,  and  also  from  sensation.     The  action 
of  the  heart  is  wholly  removed  from  the  direct  influence  of  the 
will,  and  it  is  at  least  not  obvious  that  it  is  influenced  directly 
by  sensation.     It  is  influenced  indirectly  by  both,  through  the 
agency  of  emotions  awakened  by  them.    The  muscles  of  breath- 
ing, on  the  other  hand,  though  ordinarily  involuntary,  may  be 
directly  influenced  both  by  the  will  and  by  sensation.     You 
can  at  will  breathe  faster  and  more  deeply,  and  sensations  of 
uneasiness  in  the  chest  modify  the  breathing. 


DISTINCTIONS   BETWEEN   ANIMALS   AND   PLANTS.      25 


Central  organs  of  nervous  system.     Most  developed  in  man. 

35.  For  all  these  different  actions,  thus  produced  in  different 
ways,  there  are  central  parts  of  the  nervous  system  upon  which 
the  causes  of  these  actions  produce  the  impressions  or  impulses 
from  which  the  actions  result.     Thus,  when  a  sensation  is  fol- 
lowed by  a  spontaneous  action  of  muscles,  an  impression  is 
conveyed  by  nerves  to  the  central  organ ;  the  will  there  acts, 
and  the  impulse  there  given  by  this  action  of  the  will  is  car- 
ried by  other  nerves  to  the  muscles,  which  execute  the  intended 
movement. 

36.  These  central  parts  or  organs,  which  are  the  media,  the 
instruments  of  impressions,  are  in  different  parts  of  the  body 
of  the  animal;  but  the  most  important  of  them  is  what  we 
call  the  brain.     This  part  is  developed  most  in  those  animals 
that  give  the  greatest  evidences  of  intelligence ;  and,  therefore, 
it  is  more  prominent  in  man  than  in  any  other  animal. 

37.  It  may  be  remarked,  as  a  general  truth,  that  the  nervous 
system,  and  its  associate  or  subordinate  system,  the  muscular, 
are  developed  in  different  degrees  or  forms,  to  suit  the  different 
characters  and  wants  of  animals.     In  man,  they  are  more  com- 
plex and  perfect  than  in  any  other  animal.   The  brain,  in  him,  is 
a  large  organ,  occupying  the  skull.     The  spinal  marrow,  and 
other  central  parts,  and  the  nerves,  are  largely  developed.   And 
the  muscles  which  are  moved  by  this  nervous  system  form  a 
large  portion  of  the  bulk  of  the  body.    The  organs  of  nutrition, 
analogous  to  those  which  make  up  nearly  the  whole  of  the 
plant,  occupy  the  two  cavities  of  the  trunk  of  the  body,  the 
thoracic  and  the  abdominal.     But,  as  we  descend  in  the  animal 
kingdom,  the  nervous  system  becomes  continually  less  promi- 
nent, and  the  system  of  mere  nutrition  more  so.    We  at  length 
come  to  animals,  in  which  the  nervous  system  is  a  mere  small 
appendage  to  the  system  of  nutrition,  and  only  serves  to  direct 
the  muscles  in  securing  the  food  of  the  animal.     In  some  of 
these,  we  not  only  do  not  find  a  brain,  but  we  fail  to  discover 
any  traces  of  a  nervous  system.     This  is  true  of  the  Hydra, 
noticed  in  §  29. 

38.  The  nervous  system,  which  so  clearly  distinguishes  most 
animals  from  all  plants,  is  fairly  presumed  to  exist,  though  in 
an  exceedingly  slight  degree,  in  those  beings  in  which  it  can 
not  be  found,  but  in  which  we  find  other  characteristics  of  the 
animal  kingdom.     And  it  is  presumed,  also,  that  the  exercise 
of  thought  and  the  action  of  the  will,  which  most  animals  so 
plainly  exhibit,  while  they  become  less  and  less  obvious  as  we 
descend  in  the  scale,  are  not  wholly  obliterated  in  the  very 


26  HUMAN   PHYSIOLOGY. 

No  nervous  system  in  some  animals;  yet  feeling  and  thought. 

lowest  animals.  It  may,  perhaps,  be  said,  that  as  muscular 
action,  as  mentioned  in  §  34,  is  sometimes  produced  even  in 
man  without  the  intervention  of  thought  or  the  will,  it  may  be 
produced  in  animals  of  the  lowest  order  altogether  in  this  way. 
But  we  may  more  rationally  infer  that,  as  the  chief  object  of 
motion  in  them  is  the  securing  of  food,  it  is  guided  by  the 
action  of  a  will  in  obedience  to  their  sensations.  In  other 
words,  it  is  truly  a  spontaneous,  and  not  a  mere  automatic  mo- 
tion. And  it  is  probable  that  there  is  in  the  very  lowest  of 
animals  some  degree,  though  it  may  indeed  be  slight,  of  enjoy- 
ment in  the  sensations  received  from  the  moving  water  about 
it,  and  from  the  satisfying  of  its  wants  in  the  process  of  nutri- 
tion. We  will  take  the  Hydra,  a  representation  of  which  is 
given  in  Fig.  1,  page  23,  as  an  illustration  of  the  above  remarks. 
It  is  a  minute  gelatinous  animal,  in  which  no  nervous  or  mus- 
cular fibres  can  be  found.  And  yet  it  has  an  extraordinary 
power  of  extending  and  contracting  itself.  When  it  is  alarmed, 
it  draws  in  its  arms,  and  shrinks  into  the  form  of  a  little  glob- 
ule ;  and  if  you  should  see  it  in  this  condition,  you  would  not 
suspect  that  it  had  any  arms  or  tentacula.  But  when  it  is 
searching  for  food,  it  often  extends  its  body  and  its  arms  to  a 
great  length ;  and  when  it  grasps  its  prey,  it  puts  it  into  its 
stomach,  which  constitutes,  so  far  as  we  can  see,  its  whole 
body.  We  can  not  conceive  of  all  these  motions,  thus  exe- 
cuted to  effect  certain  definite  objects,  without  the  agency  of  a 
will,  and  without  sensations  to  prompt  the  will  and  guide  the 
motions.  The  animal  must  have  a  power  of  choice,  or  it  would 
put  a  bit  of  stick  or  straw  into  its  stomach  as  readily  as  a 
worm  or  an  insect.  But  the  tentacula  never  grasp,  among  the 
various  bits  of  things  which  float  against  them,  any  thing  be- 
side the  appropriate  food  of  the  animal.  And  it  undoubtedly 
enjoys  its  food  as  really,  though  perhaps  not  as  vividly,  as  any 
human  epicure ;  and  has  in  some  measure  the  same  pleasur- 
able sensations  which  locomotion  produces  in  us,  as  it  floats 
along  so  quietly,  with  its  arms  hanging  down  from  its  body. 
Though  there  be  no  nervous  fibres  to  be  seen  in  the  loose  gela- 
tinous structure  of  this  little  creature,  yet,  as  the  phenomena 
which  it  exhibits  are  known  to  be  produced  by  the  nervous 
system  in  those  animals  whose  structure  is  more  plainly  and 
thoroughly  developed,  we  justly  infer  that  there  must  be 
nervous  matter,  in  some  form,  in  this  and  other  similar  ani- 
mals. 

39.  One  more  important  distinction  between  animals  and 


MAN  IN  HIS  KELATIONS  TO  NATUKE.  27 

Peculiar  endowments  of  man.     Abstract  reasoning.    Conscience. 

plants  remains  to  be  noticed.  It  relates  to  their  chemical  com- 
position. I  stated,  in  §  23,  that  organized  substances  are  com- 
posed mostly  of  four  elements — oxygen,  hydrogen,  nitrogen,  and 
carbon.  Plants  differ  from  animals,  in  having  but  little  nitro- 
gen in  their  composition.  It  was  formerly  supposed  that  they 
contained  none  of  this  element.  It  is  found  only  in  particular 
parts  of  plants,  as  the  seeds.  We  may  regard  carbon  as  the 
most  characteristic  constituent  of  vegetables,  and  nitrogen  of 
animals.  And  in  this  connection  it  is  interesting  to  observe 
that,  while  carbon  is  largely  thrown  off  from  the  lungs  of  ani- 
mals, in  the  shape  of  carbonic-acid  gas,  it  is  as  largely  absorbed 
by  the  leaves  of  plants.  Of  this  feet  I  shall  take  more  par- 
ticular notice  when  I  come  to  the  subject  of  respiration. 


CHAPTER  III. 

MAN  IN  HIS  RELATIONS  TO  THE  THREE  KINGDOMS  OF  NATURE. 

40.  MAN  is  commonly  spoken  of  as  being  at  the  head  of  the 
animal  kingdom,  and  in  the  book  of  the  naturalist  is  made  an 
order  of  the  class  termed  Mammalia.  As  the  basis  of  the 
whole  classification  is  mere  material  organization,  and  has  no 
reference  at  all  to  mental  or  spiritual  endowments,  the  classifica- 
tion, in  regard  to  man,  is  in  its  principle  correct.  At  the  same 
time,  it  must  be  admitted,  that  it  fails  to  recognize  altogether 
the  essential  distinctions  between  man  and  other  animals. 
These  distinctions,  making,  as  they  do,  a  wide  gap — "  an  im- 
passable chasm,"  as  Professor  Guyot  expresses  it — between  man 
and  the  inferior  animals,  are  to  be  found  in  certain  peculiar 
spiritual  endowments  which  man  possesses.  These  I  will  no- 
tice now  in  the  briefest  manner,  leaving  ij^  for  another  part  of 
this  book  to  treat  more  fully  of  this  and  other  kindred  subjects. 
One  of  these  endowments  is  the  power  of  abstract  reasoning. 
Other  animals  in  a  certain  sense  reason,  that  is,  they  make  in- 
ferences; but  they  never  arrive  at  any  general  or  abstract 
truths.  Another  endowment  is  a  moral  one,  linking  man  in  his 
spiritual  nature  to  the  Deity.  It  is  conscience,  or  the  knowledge 
and  sense  of  what  is  right,  in  distinction  from  what  is  wrong. 
Other  animals,  in  obedience  to  the  passions  of  fear  and  love, 


28  HUMAN  PHYSIOLOGY. 

Immortality.     Real  relation  to  the  animal  kingdom. 

sometimes  appear  to  the  superficial  observer  to  have  an  idea  of 
what  is  right,  as  such ;  but  there  is  not  the  slightest  evidence 
that  they  really  have  any  such  knowledge. 

41.  In  view  of  these  endowments  of  man,  it  is  wrong  to 
consider  him  merely  as  being  at  the  head  of  the  animal  king- 
dom.    He  is  something  more  than  this.     He  is  so  much  and 
so  distinctly  more,  that  the  accepted  classification  of  him,  on 
the  ground  of  mere  difference  of  organization,  gives  a  most 
inadequate  idea  of  his  true  position  in  the  scale  of  being.     It 
leaves  entirely  out  of  view  the  essential  distinctions;   and  it 
separates  man  from  other  animals,  as  you  will  see,  by  a  distinc- 
tion of  organization  which  is  of  rather  a  trivial,  perhaps  ques- 
tionable, character. 

42.  The  force  of  this  view  of  the  subject  is  enhanced,  if  we 
take  into  consideration  that  great  fact,  revealed  to  us  by  God 
in  his  Word,  that  man  is  destined  to  immortality.     It  may  be 
objected  that,  as  this  fact  is  learned  only  by  revelation,  and  not 
by  observation,  it  is  not  to  be  regarded  as  a  scientific  fact. 
But,  granting  that  there  is  truth  in  the  objection,  it  certainly 
is  allowable  to  allude  to  the  revelations  of  Scripture,  as  con- 
firming or  enforcing  views  developed  by  scientific  observation. 
This  is  all  that  I  have  done  in  this  case.     The  view  which  I 
have  presented  is  based  upon  endowments  that  are  recognized 
by  the  scientific  observer,  without  the  aid  of  revelation ;  and  I 
appeal  to  the  revealed  fact  of  man's  immortality,  as  adding 
force  to  this  view,  and  not  as  being  at  all  necessary  to  the 
establishment  of  its  truth. 

43.  Let  us  look  at  this  subject  in  another  point  of  view. 
The  grand  essential  distinction  between  animals  and  plants  lies, 
as  you  have  seen  in  the  last  chapter,  in  the  fact  that  animals 
have  a  nervous  system.     Now,  with  this  system,  as  you  have 
also  seen,  appear  certain  mental  manifestations.     These  differ 
widely  in  different  animals,  and  are  most  prominent  in  those  in 
which  this  system  is  most  prominent  and  complicated.     As  we 
trace  upward  these  complications,  when  we  come  to  man,  we 
find  certain  mental  manifestations,  which  separate  him  by  "  an 
impassable  chasm"  from  all  other  animals.     Till  we  arrive  at 
him,  the  difference  is  one  of  degree,  for  the  most  part.     But  in 
his  case  it  is  a  difference  of  kind,  and  a  very  wide  one.     Of 
such  a  difference  the  naturalist  should  certainly  take  very  dis- 
tinct cognizance ;  and,  if  it  be  not  consistent  for  him  to  do  so 
in  his  classification,  great  force  and  prominence  should  be  given 
to  these  views  in  his  instructions  on  this  subject.    As  the  super- 


MAN  IN  HIS  RELATIONS  TO  NATURE.      29 

The  hand  of  man.     No  other  animal  really  has  such  a  member. 

adding  of  the  nervous  system  separates  the  animal  from  the 
plant,  so,  also,  as  Professor  Guyot  very  justly  maintains,  the 
superadding  of  such  endowments  as  we  find  in  man  separates 
him,  by  a  chasm  quite  as  "  impassable,"  from  other  animals. 

44.  The  distinction  commonly  received  as  the  ground  of 
classification  for  man,  I  have  said,  is  a  trivial,  perhaps  a  ques- 
tionable one.  He  is  said  to  have  two  hands,  and  so  makes  the 
order  Bimana ;  while  apes  and  monkeys  are  said  to  have  four 
hands,  and  are,  therefore,  considered  as  making  the  order 
Quadrumana.  Now,  if  we  observe  carefully  and  fully  the  won- 
derful endowments  of  the  human  hand,  we  shall  hardly  be 
willing  to  allow  that  monkeys  and  apes  have  four  such  mem- 
bers. With  a  full  view  of  the  capabilities  of  the  human  hand, 
those  members  can  not  be  considered  as  hands,  but  as  members 
possessing  some  of  the  properties  of  both  hands  and  feet. 
They  are  given  to  these  animals  to  enable  them  to  climb  with 
facility,  and  to  grasp  their  food ;  and  they  have  none  of  that 
infinite  variety  of  motion,  which  is  so  striking  a  peculiarity  of 
the  hand  of  intelligent  man.  The  ground  upon  which  they 
are  said  to  have  four  hands  is  that  which  is  thus  stated  by 
Cuvier.  "  That  which  constitutes  the  hand,  properly  so  called, 
is  the  faculty  of  opposing  the  thumb  to  the  other  fingers,  so  as 
to  seize  upon  the  most  minute  objects."  No  animal  besides 
man  has  this  arrangement,  except  the  Quadrumana.  It  is 
claimed,  therefore,  that  they  have  hands,  although  they  are 
very  imperfect  when  compared  with  the  hand  of  man.  The 
imperfection  is  indeed  so  great,  as  to  make  us  at  least  reluc- 
tant to  admit  the  claim  set  up  by  the  naturalist.  "  While," 
says  Carpenter,  "  the  thumb  in  the  human  hand  can  be  brought 
into  exact  opposition  to  the  extremities  of  all  the  fingers,  whe- 
ther singly  or  in  combination,  in  those  Quadrumana  which  most 
nearly  approach  man,  the  thumb  is  so  short,  and  the  fingers  so 
much  elongated,  that  their  tips  can  scarcely  be  brought  into 
opposition,  and  the  thumb  and  fingers  are  so  weak,  that  they 
can  never  be  opposed  to  each  other  with  any  degree  of  force. 
Hence,  although  admirably  adapted  for  clinging  round  bodies 
of  a  certain  size,  such  as  the  small  branches  of  trees,  &c.,  the  ex- 
tremities of  the  Quadrumana  can  never  se:ze  any  minute  object 
with  such  precision,  nor  support  large  ones  with  such  firmness, 
as  are  essential  to  the  dexterous  performance  of  operations  for 
which  the  hand  is  admirably  adapted."  Indeed,  what  is  called 
the  thumb  of  the  Quadrumana  is  so  short  and  slender,  that  Eus- 
tachius,  the  anatomist,  very  properly  said  that,  regarded  as  an 


30  HUMAN  PHYSIOLOGY. 

Other  peculiorfties.    Chin.    Erect  posture.    Weeping  nnd  laughing. 

imitation  of  the  thumb  of  man,  it  is  a  ridiculous  affair.  I£ 
then,  we  take  into  view  the  extensive  and  varied  capabilities  of 
the  human  hand,  we  must  agree  with  Sir  Charles  Bell,  when 
he  says  that  "  we  ought  to  define  the  hand  as  belonging  exclu- 
sively to  man."  This  view  of  the  subject  has  always  impressed 
itself  upon  the  minds  of  acute  observers  in  all  ages.  Aristotle 
said,  that  man  alone  possesses  hands  deserving  of  the  name. 
Anaxagoras  said,  that  "  man  is  the  wisest  of  animals,  because 
he  possesses  hands."  And  the  opinion,  thus  uttered  by  these 
philosophers  some  centuries  before  the  Christian  era,  is  fully 
echoed  at  the  present  time. 

45.  It  would  seem,  then,  that,  if  mere  organization  be  ad- 
hered to,  as  the  basis  of  classification,  it  is  desirable  that  some 
ground  of  distinction  in  relation  to  man  be  fixed  upon,  which 
is  more  definite  than  the  commonly  received  one.     It  is  to  be 
remembered,  however,  that,  in  classification,  some  one  very  ob- 
vious peculiarity  that  presents  itself  to  the  eye  is  ordinarily 
made  use  of  as  a  mark  of  distinction,  while  accurate  and  full 
discriminations  are  followed  out  entirely  separately  from  the 
mere  classification.     This  is  done  in  the  case  of  man.     His 
structure  differs  in  many  respects  from  that  of  the  inferior  ani- 
mals.    It  would  make  this  chapter  too  long  to  point  out  all 
the  differences.     Some  of  them  are  important,  while  others  are 
not.     As  an  example  of  the  latter,  I  will  mention  the  fact,  that 
no  animal  but  man  has  a  chin.     Every  other  animal  has  its 
lower  jaw  retreating  from  the  teeth,  instead  of  projecting  for- 
ward below,  as  in  man.     One  of  the  most  important  and  strik- 
ing peculiarities  of  man's  structure  is  that  general  arrangement 
which  enables  him  to  be  in  the  erect  posture.    No  other  animal 
naturally  assumes  this  posture,  or  is  able  to  maintain  it  for  any 
length  of  time;  and  most  animals  assume  one  which  is  en- 
tirely the  opposite  of  this.     Even  the  monkey,  when  taught  by 
man  to  stand  and  walk,  is  by  no  means  erect ;  but  his  lower 
limbs  are  crooked,  and  the  moment  that  he  escapes  the  neces- 
sity of  being  an  imitator,  he  is  on  all  fours.    There  is  a  distinc- 
tion of  an  interesting  character,  which  concerns  both  the  ner- 
vous and  muscular  systems.    I  refer  to  the  fact,  that  no  animal 
tout  man  can  shed  tears,  or  perform  those  muscular  motions 
which  are  necessary  to  the  acts  of  weeping  and  laughing.     In 
view  of  this  marked  distinction,  man  has  sometimes  been  desig- 
nated as  "  a  laughing  and  crying  animal." 

46.  But  the  great  essential  distinctions,  to  which  all  the  rest 
are  really  tributary,  are,  as  I  have  before  stated,  of  a  mental  or 


MAN   IN   HIS   RELATIONS  TO   NATURE.  81 


Tendency  to  skepticism.    Robinet's  doctrines. 


spiritual  character.  And  these  should  always  be  made  peculi- 
arly prominent,  whenever  the  distinctions  between  man  ant! 
the  inferior  animals  are  treated  of  by  the  naturalist.  This 
should  be  done,  not  only  because  they  are  essential,  but  also 
because,  as  I  have  just  hinted,  all  other  distinctions  are  subor- 
dinate and  tributary  to  them.  It  is  the  mental  peculiarities  of 
man,  for  the  most  part  at  least,  that  render  necessary  those 
peculiarities  which  distinguish  his  organization  from  that  of 
other  animals.  I  will  not  dwell  on  this  point,  as  I  shall  speak 
of  it  in  another  part  of  this  book. 

47.  In  view  of  this  whole  subject,  it  may  be  said,  that  the 
classification  upon  which  I  have  commented  is  not  of  itself  of 
very  great  importance,  provided  that  the  definite  distinctions, 
which  have  been  pointed  out  as  existing  between  man  and 
other  animals,  be  clearly  recognized  by  the  naturalist.     The 
tendency,  however,  evidently  is,  to  lose  sight  of  these  distinc- 
tions in  the  exclusive  regard  which  is  paid  to  mere  material 
organization.     This  tendency,  it  is  true,  is  effectually  counter- 
acted in  the  case  of  the  great  majority  of  scientific  men,  by 
the  comprehensive  and  Christian  views  which  they  take  of  the 
whole  subject ;  but,  still,  it  manifestly  exists,  and  gives  rise  to 
many  sceptical  notions,  especially  in  superficial  and  theorizing 
observers.     Great  care,  then,  should  be  taken  to  oppose  this 
tendency  in  all  public  teaching  on  this  subject,  whether  it  be 
done  by  books  or  lectures. 

48.  There  is  a  disposition,  on  the  part  of  some  writers,  to 
obliterate  the  grand  distinction  between  man  and  the  inferior 
animals,  and  other  distinctions  which  are  stamped  by  the  Cre- 
ator upon  his  works.    Some  go  so  far  as  to  maintain,  that  there 
is  not  only  no  line  to  be  drawn  between  the  animal  and  the 
vegetable  kingdoms,  but  none  even  between  organized  and  un- 
organized  substances.      Robinet,    and   many  other  European 
authors,  teach  that  all  matter  has  living  properties,  and  that 
every  object  that  we  see,  whether  mineral,  vegetable,  or  animal, 
is  the  result  of  repeated  and  progressive  efforts  of  nature.    The 
ultimate  aim  of  these  efforts  is  considered  to  be  the  formation 
of  man,  who  is  looked  upon  as  the  perfection  of  organization 
evolved  by  these  efforts.    In  advocating  this  theory,  they  make 
great  use  of  resemblances  and  analogies,  and  even  represent 
the  fantastic  shapes  which  minerals  sometimes  assume,  from 
their  slight  resemblance  to  parts  of  the  human  body,  "  as  so 
many  proofs,"  in  the  language  of  Carpenter,  "  of  this  long  and 
bungling  apprenticeship  of  nature  to  man-making."     Although 


32  HUMAN   PHYSIOLOGY. 


Gradations  in  nature.    Wrong  ideas  of  perfection. 


such  ridiculous  doctrines  are  seldom  formally  advanced,  there  ia 
a  disposition  in  many  scientific  men  to  indulge  in  speculations 
which  have  more  or  less  resemblance  to  them.  They  seem  dis- 
posed to  confuse  with  the  veil  of  mystic  scepticism  the  clear 
characters  which  God  has  imprinted  upon  the  manifestations 
of  his  power.  It  is  well,  therefore,  to  fix  these  characters 
definitely  in  the  mind,  in  order  to  guard  against  the  fascinating 
and  bewildering  speculations  of  a  false  science.  A  true  science, 
forsaking  the  mazes  of  speculation,  and  inquiring  only  for  the 
facts,  reads  with  admiration  and  reverence  the  clear  lines  of 
God's  handiwork,  and  attributes  to  no  imaginary  agency,  termed 
Nature,  what  bears  the  marks  of  exquisite  design  and  Almighty 
power. 

49.  An  idea,  somewhat  akin  to  that  of  Robinet,  is  sometimes 
entertained,  viz.,  that  the  varieties  in  the  mineral,  vegetable, 
and  animal  kingdoms  are  mere  gradations  in  nature.     There 
would  be  some  plausibility  in  this  notion  if  it  were  difficult  to 
distinguish  the  minerals  of  the  most  perfect  kind  from  the  lowest 
plant,  and  then  the  plants  of  the  highest  order  from  the  lowest 
animal.    But  the  difficulty  lies  in  other  quarters.    The  most  per- 
fect in  the  three  kingdoms  are  distinguished  from  each  other  in 
the  most  marked  manner ;  and  it  is  only  when  the  character- 
istic qualities  are  the  least  developed  that  there  is  any  difficulty. 
One  kingdom  is  a  no  more  perfect  formation  than  another. 
The  < crystal,  with  its  exact  lines  and  angles — the  plant,  with 
its  curvilinear  and  less  definite  shapes — and  the  symmetrical 
animal,  are  equally  perfect  in  their  kind.     Each  is  made  for 
a  definite  purpose,  and  is  perfectly  adapted  to  that  purpose. 
In  none  is  there  any  imperfection  which  could  be  remedied  by 
endowments  taken  from  another  kingdom  of  nature.     In  the 
vast  variety  of  forms  which  nature  presents,  there  is  to  be  seen 
no  vain  struggling  after  a  higher  and  better  state.     There  is  no 
progressiveness,  aiming  at  an  ideal  perfection.    Neither  are  there 
gradations  leading  to  it.    All  the  works  of  the  Creator  are  per- 
fectly adapted  to  the  spheres  which  they  fill.     They  were  all, 
from  "  man,  made  in  His  image,"  down  to  the  humblest  ani- 
mal or  plant,  pronounced  to  be  "very  good,"  as  they  came 
from  His  hand. 

50.  Let  me  not  be  understood  to  say  that  there  are  no  gra- 
dations in  nature.     There  are  some  of  a  very  interesting  char- 
acter ;  but  they  do  not  obey  any  such  laws  as  those  which  are 
indicated  by  Robinet  and  other  fanciful  theorizers.     There  are 
gradations  in  both  the  animal  and  vegetable  world.     You  ob- 


MAN  IN  HIS   RELATIONS  TO  NATURE.  33    * 

Man  inferior  to  other  animals  in  some  respects. 


serve  them  as  you  go  from  the  simplest  plant  up  to  the  most 
complicated.  And  so  of  animals.  But  these  two  kingdoms 
of  nature  are  separate  in  their  gradations,  and  are  not  in  one 
series  together,  as  is  represented  by  Robinet.  And  the  grada- 
tion in  each  kingdom  is  by  no  means  an  unbroken  and  regular 
one,  going  up,  step  by  step,  from  the  lowest  to  the  highest. 
For  example,  in  the  animal  kingdom,  there  are  not  constant 
and  regular  additions  made,  as  you  trace  the  gradations  up- 
ward. And  though  man  stands  at  the  top  of  the  series,  it  is 
not  as  a  compound,  made  up  of  all  the  excellencies  found 
below  him,  with  additional  excellencies  peculiar  to  himself. 
Superior  as  he  is,  as  a  whole,  to  all  other  animals,  yet  in  some 
respects  he  is  inferior  to  many  of  them.  He  is  inferior  to  them 
in  the  wonderful  capabilities  of  instinct.  Some  animals  can  do 
some  things  better  than  he  can.  The  monkey  is  a  better 
climber.  Some  animals  can  do  what  he  can  not.  Birds  and 
winged  insects  fly,  but  he  can  not.  These  points  could  be 
illustrated  to  any  extent,  but  this  will  suffice. 

51.  Man  is  often  spoken  of  as  being  the  most  perfect  of  ani- 
mals.    This,  as  you  will  see  from  what  was  said  in  a  previous 
paragraph,  is  not  true  in  the  strict  sense  of  the  word.     His 
organization  is  more  complicated,  and  he  has  more  and  higher 
endowments  than  any  other  animal ;  but  the  perfection  of  struc- 
ture, and  of  adaptation  in  contrivance  to  the  purposes  aimed 
at,  is  as  manifest  in  all  the  varieties  of  animals  as  it  is  in 
man. 

52.  In  one  respect,  there  is  a  gradation  existing  through  the 
three  kingdoms  of  nature.     It  is  in  regard  to  formation  or  nu- 
trition.    All  the  elements  which  are  found  in  the  composition 
of  animals  exist  in  the  mineral  world.     But  these  elements, 
with  very  few  exceptions,  can  not  be  transmitted  directly  to 
animals,  but  they  are  transmitted  indirectly  through  vegeta- 
bles.    No  animal,  therefore,  can  live  on  mineral  substances, 
although  these  substances  contain  all  the  elements  found  in  its 
composition.     But  vegetables  draw  their  nutriment  from  the 
mineral  world,  and  then  furnish  nutriment  to  animals.     There 
is,  therefore,  in   relation   to  formation,  a  gradation  running 
through  the  three  kingdoms,  from  the  mineral  up  to  the  ani- 
mal. 

53.  At  the  summit  of  the  last  step  in  this  gradation  stands 
man.     To  him,  not  only  is  the  animal  kingdom  tributary,  but 
so,  also,  are  the  mineral  and  vegetable  kingdoms.    They  are  all 
made  for  him,  to  beautify  and  gladden  this  his  temporary  home, 


34  HUMAN  PHYSIOLOGY. 

All  nature  tributary  to  man.    Imperfectly  so. 

and  to  sustain  him  in  it.  The  subjection  of  them  to  him  was 
undoubtedly  perfect  in  his  primeval  condition  of  innocence  in 
the  garden  of  Eden.  But  now,  we  see  this  tributary  subjection 
manifested  only  as  a  general  fact,  with  many  exceptions.  These 
mark  this  life  as  the  imperfect  state,  and  this  world  as  the 
temporary  home  of  man,  in  which  he  can  prepare  himself 
for  the  perfect  and  everduring  state  and  home  of  another  life 
beyond. 


PART  SECOND. 


CONTAINING, 

CHAPTER  IV.— GENERAL  VIEWS  OF  PHYSIOLOGY,  WITH  A  BRIEF  ACCOUNT  OF  SOME  OF  TH« 
STRUCTURES  IN  THE  BODY.  CHAPTER  V.— DIGESTION.  CHAPTER  VI.— CIRCULATION. 
CHAPTER  VII.-RJCSPIRATION.  CHAPTER  VIlI.-FoRMATiON  AND  REPAIR.  CHAPTER 


CHAPTER  IV. 

GENERAL  VIEWS  OF  PHYSIOLOGY,  WITH  A  BRIEF  ACCOUNT  OF  SOME 
OF  THE  STRUCTURES  IN  THE  BODY. 

54.  THE  contents  of  the  previous  chapters  are  preliminary 
to  the  consideration  of  the  real  subject  of  this  work,  the  Physi- 
ology of  Man.     But  they  were  necessary,  in  order  to  accomplish 
a  very  prominent  object  which  I  have  in  view.     It  is  my  wish 
that  the  student,  as  he  examines  the  functions  of  the  human 
system,  should  at  the  same  time  observe  the  analogies  existing 
between  man  and  other  living  beings,  in  the  processes  of  life. 
He  will,  in  this  way,  get  an  enlarged  view  of  man  in  his  rela- 
tions to  the  world  around  him,  and  will  be  prompted  to  observe 
the  phenomena  of  life,  in  whatever  department  of  nature  they 
may  be  presented  to  his  view.     And,  in  order  to  promote  this 
object  effectually,  I  shall,  as  I  proceed  with  the  development  of 
the  physiology  of  man,  refer  occasionally  to  the  analogous  phe- 
nomena in  other  animals,  and  also  in  plants.     This  will  serve 
to  fix  more  definitely  in  the  mind  of  the  student  the  main  facts 
that  are  to  be  communicated,  at  the  same  time  that  the  bound- 
aries of  his  knowledge  will  be  extended  over  fields  full  of  in- 
terest. 

55.  This  is  a  work  on  Physiology,  and  not  on  Anatomy. 
Physiology  treats  of  the  offices  or  functions  of  the  different 
parts  of  the  structure,  while  Anatomy  has  regard  to  the  struc- 
ture itself.     In  the  following  pages,  I  shall  introduce  the  anat- 
omy of  the  system  only  so  far  as  it  is  necessary  to  elucidate  its 
physiology. 

Before  proceeding  to  an  examination  of  the  individual  sub- 
jects which  will  claim  our  attention,  it  will  be  proper  to  present 
some  general  views  of  them  in  their  relations  as  a  whole. 


36  HUMAN   PHYSIOLOGY. 

Natural  division  of  the  subject.     Interest  of  the  study. 

56.  You  have  seen,  in  the  preliminary  chapters,  that  organ- 
ized living  beings  have  much  that  is  common  to  them  all.    This  is 
true  so  far  as  nutrition  is  concerned.     You  have  seen  that  the 
animal  grows  very  much   as   the  plant  does,  and    that  the 
arrangements  for  its  growth  vary  from  those  of  the  plant  only 
so  far  as  the  difference  of  the  source  of  its  nourishment,  and  of 
the  circumstances  under  which  it  is  obtained,  require.     The 
grand  distinction,   as   you   have   seen,  between    animals    and 
vegetables  is  to  be  found  in  the  functions  belonging  to  the 
nervous  system.     These  functions  are  wholly  separate  from  the 
nutritive  functions,  which  animals  perform  in  common  with 
plants. 

57.  This  view  of  the  subject  suggests  a  natural  division  of 
the  physiology  of  man  into  two  parts,  viz.,  the  nutritive  func- 
tions, and  the  animal  functions,  or  those  connected  with  the 
nervous  system.     In  other  words,  the  first  division  will  com- 
prise all  those  subjects  which  relate  to  the  building  and  repair- 
ing  of  the  human  structure  ;  and  the  second  will  comprise  those 
which  relate  to  the  uses  for  which  the  structure  is  made.     The 
first  class  of  subjects  includes  digestion,  circulation,  respiration, 
formation,  and  excretion.    The  second  class  includes  locomotion, 
sensation,  the  five  senses,  the  voice,  instinct,  thought,  &c. 

58.  The  student  will  see  at  one  glance,  that  a  wide  range  of 
exceedingly  interesting  subjects  opens   before  him.     Contem- 
plated as  a  mere  mechanism,  the  human  system  is  full  of  won- 
ders.    The  principles  of  common  Mechanics,  of  Hydraulics,  of 
Pneumatics,  of  Optics,  of  Acoustics,  are  abundantly  illustrated 
in  the  human  body,  by  contrivances  of  the  most  exact  and  ex- 
quisite adaptation.    But  this  congeries  of  beautiful  mechanisms 
is  all  regulated  by  a  nervous  system,  making  it,  by  its  minute 
fibrils,  to  be  alive  with  feeling  in  every  part.     Sensation  and 
sympathy  govern,  through  the  nerves,  in  a  wonderful  manner, 
the  ever-varying  adjustments  of  all  the  parts  of  the  complicated 
system.     It  is  not  only  mechanism,  but  living  mechanism,  that 
develops  to  us  its  wonders,  so  numerous  and  diversified.     And 
then,   when  we  look  at  the  soul — "that  side  of  our  nature 
which  is  in  relation  Avith  the  Infinite" — connected  as  it  is  by 
the  nerves  with  every  part  of  this  mechanism,  the  interest  of 
the  study  before  us  appears  exceedingly  great,  and  its  variety 
never  ending.    The  study  is  a  peculiar  one.     It  is  not  the  body 
merely  that  you  are  to  study  in  these  pages ;  but  it  is  the  body 
and  spirit  united.     The  study  differs  from  all  others  in  this 
-3spect.     In  other  studies,  you  look  at  either  matter  alone,  or 


GENERAL   VIEWS.  37 


Bones.    Two  parts,  animal  and  mineral.    Cartilages. 


spirit  alone ;  but  here  you  look  at  them  both,  as  brought  to- 
gether in  mysterious  union. 

59.  It  will  be  proper,  here,  to  say  something  in  general  of 
the  structure  of  the  human  frame,  before  proceeding  to  a  par- 
ticular view  of  individual  subjects.     I  do  this  in  order  to  avoid 
a  frequent  turning  aside  for  explanation,  which  would  not  only 
be  inconvenient,  but  would  mar  the  interest  of  the  study.     It 
will  not  be  necessary  to  go  into  a  full  description  of  the  nume- 
rous and  diverse  textures,  or  tissues,  (as  they  are  commonly 
called,)  of  the  body.     I  will  notice  only  some  of  the  principal 
of  them. 

60.  From  the  osseous  or  bony  tissue,  the  solid  part  of  the 
framework  of  the  body  is  made.     Bone  is  composed  in  part 
of   animal    matter,   and    in    part   of   mineral.      The   mineral 
part  is  mostly  phosphate  of  lime.     These  two  parts  of  bone 
are  in   different    proportions    to    each  other   in    the    different 
periods  of  life.     The  mineral  part  in  the  child  is  about  one- 
half  of  the  bone ;   in  the   adult,  four-fifths ;   and  in  the  old, 
seven-eighths.     The  bones  are  therefore  very  brittle  in  old  age, 
while  they  are  somewhat  yielding  in  childhood.     The  mineral 
and  the  animal  portions  of  bone  can  be  separated  from  each 
other.     If  a  bone  be  put  into  diluted  muriatic  acid,  the  mineral 
part  will  after  a  time  become  united  with  the  acid,  and  the 
animal  part  will  be  left,  having  the  perfect  shape  of  the  bone. 
Thus  separated  from  the  mineral  part,  it  is  so  flexible,  that  it 
can  be  tied  into  a  knot  without  affecting  its  shape.     On  the 
other  hand,  by  subjecting  a  bone  for  some  time  to  the  action  of 
heat,  the  animal  part  can  be  removed,  and  the  mineral  part  be 
left  by  itself. 

61.  The  animal  part  of  bone  is  cartilage,  or  gristle.     This 
part  is  formed  first,  constituting  a  sort  of  mould,  in  which  the 
bone  is  to  be  formed.     The  mineral  matter  is  gradually  depos- 
ited in  the  cells  of  the  cartilage.     In  the  very  young  child,  you 
can  see  that  this  process  is  not  completed,  especially  if  you  ob- 
serve the  bones  of  the  head.     The  bones  are  not  united  to- 
gether, as  they  are  in  the  adult;  and  there  is  so  little  of  mineral 
matter  near  their  edges,  that  they  can  be  bent  with  a  very 
slight  pressure.     The  proportion  of  mineral  matter  which  is 
deposited  in  the  cartilaginous  bones  varies  much  in  different 
animals.     In  many  fishes,  there  is  almost  none  of  this  deposit, 
the  skeleton  retaining   its  cartilaginous  character  throughout 
life. 

62.  Besides  the  cartilaginous  portion  of  bones,  there  are  car- 

4 


38  HUMAN"  PHYSIOLOGY. 

Ligaments.     Muscles.    Tendons.     Cellular  tissue. 

tilages  which  are  destined  to  remain  so,  instead  of  having 
mineral  deposits  made  in  their  cells.  The  ends  of  the  bones 
are  tipped  with  them.  They  are  placed  between  all  the  twenty- 
four  bones  of  the  spinal  column.  They  form  the  connecting 
links  between  the  breastbone  and  the  ribs.  Cartilage  consti- 
tutes the  body  of  the  outer  ear,  of  the  eyelids,  and  of  the 
lower  part  of  the  nose.  The  transparent  part  of  the  eye  is 
formed  of  cartilage.  This  substance  is  placed  wherever  firm- 
ness and  tenacity  are  required  without  hardness. 

63.  The  bones  are  united  together  by  ligaments  of  various 
degrees  of  strength,  according   to  the  necessity  of  the  case. 
They  are  moved  by  muscles,  which,  in  man,  are  bundles  of 
reddish  fibres.     Muscular  substance  is  what  is  commonly  called 
the  meat  in  animals.      It  is  of  various  colors  in  different  ani- 
mals, or  in  the  same  animal  at  different  periods  of  life.     All 
motion  in  animals  is  produced  by  muscles.     I  will  not  go  into 
an  explanation  of  their  action  now,  any  further  than  to  say, 
that  they  act  by  contracting  or  shortening  their  fibres.     Com- 
monly there  are  tendons  united  with  the  muscles.     These  ten- 
dons are  composed  of  strong  white  fibres,  and  have  no  power 
of  contraction  themselves.      They  serve  merely  as  the  cords 
by  which  the  contracting  muscles  move  the  bones  and  other 
pails. 

64.  The  most  common  tissue  in  the  body  is  what  is  called 
by  the  names,  cellular  membrane,  cellular  tissue,  and  areolar 
tissue.    This  last  name  is  most  commonly  used  by  physiologists 
at  the  present  time.     The  word  areolar  comes  from  the  Latin 
word  areola,  meaning  a  small  open  space.     The  term  is  appro- 
priate, because  this  tissue  is  filled  with  minute  spaces  or  cells. 
The  word  cellular  is  quite  as  appropriate ;  and,  as  this  will  be 
more  familiar  to  you,  I  shall  make  use  of  it  whenever  I  shall 
have  occasion  to  speak  of  this  tissue.     That  you  may  under- 
stand what  this  tissue  is,  I  will  refer  you  to  its  appearance  as 
you  see  it  in  different  meats.     It  is  the  delicate  white  substance 
that  you  see  between  the  different  layers  of  muscle  in  a  piece 
of  meat.      If  you  notice   particularly,  you  will  see  that  it  is 
also  between  all  the  different  fibres  of  the  muscles.     As  the 
spaces  or  cells  communicate  together,  butchers  sometimes  "  blow 
up  "  this  tissue  in  veal,  in  order  to  make  the  meat  look  more 
plump.     This  tissue  is  the  universal  packing  material  of  the 
body.     It  is  to  be  found  almost  everywhere.      It  surrounds 
every  thing, — vessels,  nerves,  muscles,  organs,  &c.     It  enters 
into  their  composition,  uniting  together  different  tissues,  and 


GENERAL  VIEWS. 


39 


Communication  between  cells  of  cellular  tissue.    Shown  in  dropsy. 

also  the  fibres  of  the  same  tissue.  It  varies  much  in  its  com- 
pactness in  different  parts.  It  is  very  fine  and  compact  where 
it  is  necessary  that  it  should  be  so  ;  while  in  other  cases  it  is 
loose  and  delicate,  allowing  a  free  motion  of  the  parts  which  it 
envelops  and  connects  together.  It  is  abundant  and  loose 
among  the  muscles,  and  between  them  and  the  skin.  Fig.  2 
represents  a  portion  of  cellu- 
lar tissue,  inflated  and  dried,  FIG.  2. 
exhibiting  the  arrangement 
of  its  larger  meshes.  This 
ia  magnified  twenty  diame- 
ters. The  free  communica- 
tion which  exists  between 
the  interstices  or  cells  in  this 
tissue  is  exemplified  in  drop- 
sy. These  cells  are  bathed, 
in  the  healthy  state,  with  a 
small  amount  of  a  watery 
fluid ;  and  when  this  in- 
creases largely,  forming  the 
disease  termed  dropsy,  it 
obeys  the  force  of  gravity  in 
the  cells,  and  accumulates 
most  in  the  lowest  parts  of 
the  lower  extremities.  This 
tissue  is  very  elastic  in  health, 
so  that  if  you  press  on  the 
skin,  there  is  no  indentation  left  when  the  pressure  is  taken 
away,  for  the  elastic  cellular  tissue  at  once  rises  from  its  state 
of  compression,  pushing  the  skin  before  it.  But  in  dropsy  it 
loses  its  elasticity  by  over  distension ;  therefore  there  is  pitting, 
as  it  is  termed,  after  removing  the  pressure.  We  sometimes 
have  an  opportunity  of  seeing  the  communication  between  the 
cells  manifested  by  the  introduction  of  air  into  them.  This  has 
occurred  in  some  cases  in  which  an  opening  has  been  made,  by 
disease  or  accident,  from  the  air  tubes  in  the  lungs  into  the  cel- 
lular tissue  in  the  walls  of  the  chest.  The  whole  body  has 
been  seen  largely  swollen,  from  the  air  which  has  from  this 
cause  accumulated  in  this  tissue  directly  under  the  skin. 
Among  the  many  tricks  of  impostors,  the  inflation  of  the  cel- 
lular tissue  of  the  head  has  been  practised ;  and  as  it  produces 
a  frightful  appearance,  and  therefore  excites  pity,  the  trick  is  a 
very  successful  one. 


CELLULAR    TISSUE. 


40  HUMAN  PHYSIOLOGY. 

Deposits  of  vat.    Its  uses.    How  kept  in  its  cells.    Mucous  tissue. 

65.  There  are  here  and  there  in  the  cellular  tissue  deposits 
of  fat.    Various  purposes  are  answered  by  these  deposits.    They 
are  sometimes  of  use  in  promoting  a  free  motion  of  the  adja- 
cent parts.     The  eye  has,  intervening  between  it  and  the  bony 
socket,  a  cushion  of  fat,  on  which  it  rests,  and  against  which 
it  is  pressed  when  any  violence  is  offered  to  it.     Fat,  as  a  non- 
conductor, is  a  protection  against  the  cold,  and  it  is  therefore 
deposited  largely  in  the  cellular  tissue  under  the  skin,  in  ani- 
mals that  inhabit  cold  climates.     Fat,  also,  sometimes  serves  as 
nourishment  to  the  system  when  its  necessities  require  it.     In 
diseases  in  which  food  cannot  be  taken  in  any  amount,  the 
fat  is  absorbed  into  the  system.      The  heat  of  the  body  is 
maintained  also,  in  part,  by  this  process.     This  occurs  in  the 
torpid  condition  of  hybernating  animals.     They  commonly  be- 
come very  fat  in  autumn,  as  a  preparation  for  the  winter,  and 
in  the  spring  they  come  forth  very  lean,  their  store  of  fat  having 
been  used  up  for  the  purposes  of  nutrition  and  heat  during 
their  confinement.     The  fat  thus  deposited  in  the  cellular  mem- 
brane or  tissue  is  not  diffused  merely  in  the  interstices,  but  it  is 
confined  in  cells  of  its  own,  which  lie  in  these  interstices.     Mi- 
nute blood-vessels  pass  from  the  fibres  of  the  cellular  tissue  to 
these  fat  cells.     The  fat,  which  is  an  oily  fluid,  is  kept  from 
oozing  through  the  pores  of  the  cells  that  hold  it  by  the  blood, 
which  is  very  nearly  four-fifths  water,  and  by  the  watery  fluid 
which  I  have  spoken  of  as  bathing  all  the  interstices  of  the 
cellular  tissue ;  for  oil,  you  know,  will  not  pass  through  any 
porous  substance  that  is  wet  with  any  watery  fluid.     If  a  por- 
tion of  cellular  membrane  containing  fat  be  dried,  the  fat,  which 
in  the  moist  state  is  wholly  confined  to  its  cells,  now  oozes 
through  their  pores.     This  is  the  reason  that  a  lump  of  fat,  as 
it  is  called,  feels  so  oily  after  it  has  been  exposed  for  a  while  to 
the  air. 

66.  The  mucous  tissue  is  that  which  lines  all  the  cavities  of 
the  body  that  have  outlets.     It  lines  the  mouth  and  the  cavities 
of  the  nose,  and  descends  into  the  lungs,  the  stomach,  &c.     It 
takes  its  name  from  the  fluid  called  mucus,  which  is  constantly 
secreted  by  innumerable  minute  glands,  that  are  situated  in  the 
substance  of  this  membrane.     The  chief  object  of  this  viscid 
fluid  is  to  protect  the  membrane  from  the  substances  which 
come  in  contact  with  it,  which  would  otherwise  produce  some 
irritation.     This  membrane  is  continuous  with  the  skin,  shading 
off  into  it  insensibly,  as  you  may  observe  on  the  lips. 

67.  The  serous  tissue  or  membrane  forms  the  outer  coat  or 


GENERAL   VIEWS.  41 


Serous  membranes.     Compound  character  of  the  organs. 

lining  of  nearly  all  those  organs  the  inner  coat  of  which  is  mu- 
cous membrane.  This  is  the  case  with  the  lungs,  the  stomach, 
and  the  intestines.  The  serous  membranes  are  white,  smooth, 
and  shining,  and  are  lubricated  with  a  watery  fluid,  called 
serum.  Every  serous  membrane  forms  a  cavity  or  sac  without 
.an  outlet,  differing  in  this  respect  entirely  from  the  mucous 
membranes.  Thus,  in  the  case  of  the  lungs,  the  serous  mem- 
brane lining  the  outside  of  each*  of  these  organs  passes  from 
the  lungs  to  the  walls  of  the  chest,  lining  the  inside  of  them, 
arid  thus  makes  a  sac  without  an  outlet  for  each  lung.  This 
sac  could  be  dissected  off,  and  taken  out  whole.  When  the 
fluid  which  lubricates  the  inside  of  this  sac  increases  to  any 
extent,  the  disease  called  dropsy  in  the  chest  is  produced.  The 
membrane  which  thus  lines  the  outside  of  the  lungs  and  the 
inside  of  the  walls  of  the  chest  is  called  the  pleura,  and  it  is  the 
seat  of  the  disease  termed  pleurisy. 

68.  I  have  thus  described  some  of  the  principal  of  the  tis- 
sues which  make  up  the  human  structure.     The  other  tissues 
will  be  spoken  of  in  the  proper  connection  as  we  proceed.     Be- 
fore dismissing  this  subject,  I  will  call  your  attention  to  the  fact, 
that  the  organs  of  the  body  are  generally  composed  of  several 
tissues  united  together.     Thus,  the  stomach  has  three  coats,  as 
they  are  termed, — the  mucous  as  the  inner  coat,  the  serous  as 
the  outer,  and  the  muscular  between  them.    And  then  we  have 
the  cellular  tissue  uniting  these  together.     Besides  these,  there 
are  arteries,  and  veins,  and  nerves,  so  that  the  stomach,  which 
looks  like  a  simple  pouch,  is  really  quite  a  composite  thing. 
And  the  same  can  be  said  of  the  other  organs. 

69.  Before  entering  upon  the  particular  consideration  of  the 
functions  by  which  the  system  is  built  up  and  kept  in  repair, 
it  will  be  well  to  take  a  general  view  of  them,  that  you  may 
see  them  in  their  connection  and  mutual  dependence.     Each 
of  these  functions  has  its  special  and  appropriate  part  to  play, 
in  effecting  the  formation  and  repair  of  the  structure.     The 
material  from  which  all  parts  of  the  body  are  formed  and 
repaired  is  the  blood.     There  are  organs  whose  special  duty  it 
is  to  make  this  material ;  organs  which  distribute  it ;  and  or- 
gans which  use  it  after  it  is  distributed.     There  are  also  organs 
whose  duty  it  is  to  receive  the  blood  after  it  has  been  used,  and 
fit  it  to  be  used  again.     This  common  building  material  of  the 
body  is  made  out  of  the  food ;  and  the  succession  of  processes 
by  which  it  is  done  I  will  describe  in  the  next  chapter.     After 
it  is  made,  it  is  distributed  by  the  complicated  apparatus  of  the 

4* 


42  HUMAN   PHYSIOLOGY. 


Summary  of  nutritive  functions.     Processes  of  digestion. 


circulation.  This  apparatus  is  therefore  the  common  carrier  of  the 
building  material  of  the  system.  It  is  the  numberless  little  form- 
ative vessels,  so  small  as  to  be  invisible  to  the  naked  eye,  that 
use  the  blood  thus  brought  to  them,  and  make  and  keep  in 
repair  all  the  various  structures  that  we  see  in  the  body.  When 
the  blood  has  been  used  by  these  formative  vessels,  it  is  not  fit 
to  be  used  again  until  it  is  submitted  to  a  purifying  process  by 
exposure  to  air ;  and  to  this  particular  object  the  lungs  are  de- 
voted. And  besides  all  this,  as  there  are  continually  some  par- 
ticles which,  in  the  wear  and  tear  of  the  machinery,  become 
useless,  and  even  injurious,  they  must  be  got  rid  of  in  some 
way;  and  so  there  are  organs  for  this  purpose — organs  of 
waste,  as  they  are  termed.  It  is  also  to  be  remembered,  that 
the  processes  to  which  I  have  now  alluded  are  so  carried  on, 
that  the  heat  of  the  body,  as  will  be  fully  explained  hereafter, 
is  steadily  maintained.  In  the  following  chapters  of  this  part, 
I  proceed  to  a  particular  examination  of  the  functions  of  which 
I  have  now  given  a  brief  summary. 


CHAPTER  V. 

DIGESTION. 

70.  I  SHALL  include,  under  the  term  digestion,  all  those  pro- 
cesses which  are  necessary  to  effect  the  separation  from  the 
food  of  its  nutritious  portion,  and  the  introduction  of  it  into  the 
circulation.  A  summary  of  these  processes  may  be  thus  given. 
The  food  is  broken  up  and  ground  in  the  mouth,  and  it  is  at 
the  same  time  mixed  with  the  saliva.  It  is  then  taken  into  the 
stomach,  where  it  is  kept  in  constant  motion,  and  is  under  the 
solvent  action  of  a  fluid  of  a  peculiar  character.  When  it  is 
brought  into  the  right  condition,  it  is  passed  from  the  stomach 
into  the  intestines.  Here  it  is  acted  upon  by  two  fluids,  the 
bile,  the  secretion  of  the  liver,  and  the  secretion  of  another 
gland,  the  pancreas  or  sweet-bread.  These  secretions  have 
some  agency  in  separating  from  the  mass  its  nutritious  portion, 
and  this  is  taken  up  or  absorbed,  in  the  form  of  a  milky  fluid, 
by  little  vessels  lying  on  the  surface  of  the  inner  membrane  of  the 
intestine.  These  vessels  unite  together  to  form  a  large  tube, 
and  through  this  the  milky  fluid  is  poured  into  the  circulation, 
to  replenish  the  blood. 


DIGESTION.  43 


Mastication.    Teeth  various,  according  to  different  kinds  of  food. 

Having  given  this  summary  of  the  processes  which  make  up 
digestion,  I  proceed  to  speak  of  them  more  particularly  in  the 
Border  of  their  succession.  In  doing  so,  I  shall  notice  some  of 
the  points  in  which  other  animals  differ  from  man,  in  regard  to 
these  processes  and  the  arrangements  of  the  apparatus  of  diges- 
tion. 

71.  Mastication  is  an  important  part  in  the  process  of  diges- 
tion. The  teeth,  which  perform  this  act,  are  very  hard  bodies. 
The  body  of  a  tooth  is  composed  of  two  substances.  The  in- 
ner part  is  called  the  ivory,  and  the  outer  is  called  the  enamel, 
which  is  exceedingly  hard.  The  teeth  are  of  different  shapes 
for  different  modes  of  action.  There  are  long  and  pointed 
teeth,  for  tearing;  others,  for  cutting,  which  have  a  sharp  edge; 
and  others,  for  grinding,  having  for  this  purpose  a  broad  and 
irregular  surface.  The  teeth  are  differently  shaped  in  animals, 
according  to  the  kinds  of  food  which  they  eat.  Thus,  the  her- 
bivorous, or  vegetable-eating  animals,  have  grinding  teeth  to 
bruise  their  food ;  while  the  carnivorous,  or  flesh-eating  animals, 
have  sharp-edged  teeth  and  long-pointed  teeth,  by  which  their 
food  is  torn  and  cut  in  pieces.  And  it  is  to  be  observed,  that 
the  movement  of  the  jaws  always  corresponds  with  the  char- 
acter of  the  teeth.  In  the  carnivorous  animals,  the  motion  of 
the  lower  jaw  upon  the  upper  is  a  mere  up-and-down,  or  hinge- 
like  motion.  As  they  have  no  grinding  teeth,  there  is  no 
need  of  any  lateral  or  grinding  motion.  But  in  the  animals 
that  have  grinding  teeth,  there  is  a  lateral  motion,  to  enable 
them  to  grind.  You  see  this  difference  very  plainly,  if  you  ob- 
serve the  dog  and  the  horse  while  they  are  eating.  In  Fig.  3, 
you  see  represented  the  teeth  of  a  carnivorous  animal.  The 
front  teeth  are  long  and  pointed,  for  rending,  while  the  back 

FIG.  3. 

FIG.  4. 


TEETH  OF  HERBIVOROUS 
ANIMAL. 


TEETH  OF  CARNIVOROUS  ANIMAL. 


44  HUMAN   PHYSIOLOGY. 


Man  an  omnivorous  animal. 


teeth  have  a  sharp  edge  for  cutting.  In  Fig  4,  you  see  repre- 
sented the  broad  and  irregular  grinding  surfaces  of  the  teeth  of 
herbivorous  animals.  In  animals  that  live  on  insects,  the  teeth 
present  conical  points,  which  press  into  corresponding  depres- 
sions in  the  opposite  jaw,  as  represented  in  Fig.  5,  In  those 
that  live  on  soft  fruits,  the  teeth  are  rounded,  as  in  Fig.  6. 
These  are  quite  in  contrast  with  the  tearing  teeth  of  the  carniv- 
orous, and  the  grinding  teeth  of  the  herbivorous. 

FIG  5.  FIG.  6. 


TEETH  OF  INSECTIVOROUS  ANIMAL. 


TEETH   01'  FRUGIVOROU3 
ANIMAL. 


*72.  There  is  an  arrangement  of  the  enamel  and  the  ivory  in 
the  teeth  of  the  herbivorous  which  ought  not  to  pass  unnoticed. 
Instead  of  having  the  enamel  cover  the  ivory,  as  in  the  teeth 
of  the  carnivorous,  the  two  substances  are  arranged  in  upright 
layers,  as  seen  in  Fig.  4.  The  object  of  this  is  plain.  The 
ivory  wears  away  faster  than  the  harder  enamel,  and,  therefore, 
the  surface  of  the  tooth  always  presents  projecting  hard  ridges, 
fitting  them  for  grinding  thoroughly.  A  miller  would  say,  that 
these  are  stones  that  never  need  picking. 

73.  So  perfect  is  the  correspondence  of  the  teeth  with  the 
kind  of  food  on  which  the  animal  lives,  that  the  skillful  natural- 
ist can  infer  very  correctly,  from  the  examination  of  the  teeth 
of  an  animal  alone,  the  character  of  the  food  on  which  it  lives, 
and  even  the  general  arrangement  of  its  structure.  As  man 
has  the  three  kinds  of  teeth  which  I  have  noticed,  he  is  said  to 
be  omnivorous,  or  an  eater  of  all  kinds  of  food  In  him,  the 
front  teeth  are  the  cutting  ones ;  what  are  called  the  stomach 
and  eye  teeth  are  the  tearing  ones ;  and  the  large  back  teeth 
are  shaped  for  grinding.  It  will  be  observed  that  the  tearing 
teeth,  as  they  have  not  a  very  sharp  point,  and  are  no  longer 
than  the  other  teeth,  have  but  little  power  when  compared  with 
the  long  and  sharp  tearing  teeth  of  a  carnivorous  animal,  as 
seen  in  Fig.  3.  As  man  can  make  use  of  instruments  to  cut 


DIGESTION.  45 


Wliales  have  no  teeth.    Substitute  for  teeth  in  birds 


his  food  in  pieces,  he  does  not  need  such  power  in  his  teeth  as 
carnivorous  animals  have.  Allowance  should  be  made  for  this 
in  estimating  the  amount  of  carnivorous  adaptation  in  man. 

74.  There  are  a  few  of  the  Mammalia  that  have  no  teeth. 
This  is  the  case  with  the  common  whale.  In  his  case,  instead 
of  teeth,  there  hang  down  from  the  upper  jaw,  as  represented 
in  Fig.  7,  plates  of  a  fibrous  substance,  called  whalebone,  which 
have  their  fibres  separated  at  their  free  extremities,  so  as  to 
make  a  sort  of  sieve.  This  is  intended  to  catch  the  little  gela- 
tinous animals,  which  the  whale  devours  in  great  numbers. 

FIG.  8.  FIG.  7. 


•WHALEBONE.  SKULL  OF  WHALE. 

For  this  purpose,  he  draws  in  the  water,  making  it  to  pass 
through  this  sieve,  and  then  expels  it  from  the  nostrils  or  blow- 
holes. Birds,  too,  have  no  teeth.  Their  place  is  supplied 
by  a  contrivance  in  the  stomach  itself,  for  the  breaking  up  of 
the  food.  This  will  be  described  in  another  part  of  this 
chapter. 

75.  While  the  food  is  cut  and  ground  by  the  teeth,  it  is  at 
the  same  time  thoroughly  moistened  by  the  saliva,  which  is 
poured  forth  from  certain  glands  in  the  neighborhood.  There 
are  three  pairs  of  these  glands.  Fig.  9  shows  the  glands  on 
one  side.  The  parotid  gland,  1,  is  the  largest.  This  is  situated 
in  front  of  the  lower  part  of  the  ear.  It  is  the  seat  of  the 
swelling  in  the  disease  called  mumps.  Its  duct,  2,  passes  over 
one  large  muscle  and  between  the  fibres  of  another,  and  pours 
its  contents  into  the  mouth  opposite  the  second  small  grinder  of 
the  upper  jaw.  If  you  press  on  this  part  of  the  cheek,  you  can 


46 


HUMAN  PHYSIOLOGY. 


Formation  of  the  saliva.     Three  pairs  of  salivary  glands. 


FIG.  9. 


SALIVARY    GLANDS. 


feel  in  the  mouth  an  increased  flow  of  the  saliva.  The  sub- 
maxillary  gland,  3,  is  situated  inside  of  the  lower  jaw  at  its 
lower  part ;  and  its  duct,  4,  opens  into  the  mouth  at  the  side 
of  the  framum  of  the  tongue.  The  sublingual  gland,  5,  lies 
under  the  tongue,  and  discharges  its  secretion  by  a  duct  at  the 
side  of  that  organ.  These  saliva  factories,  as  we  may  term 
them,  are  in  much  more  active  operation  at  some  times  than 
at  others.  They  are  especially  active  when  we  are  eating  ;  and 
it  is  commonly  estimated  that,  during  an  ordinary  meal,  about 
eight  ounces  of  saliva  are  poured  into  the  mouth.  This  large 
amount  is  wanted  to  moisten  the  food  thoroughly  before  it  is 
swallowed ;  and  it  is  supposed,  also,  that  it  has  some  chemical 
influence  in  preparing  the  food  for  the  action  of  the  gastric 
juice  in  the  stomach.  More  saliva  than  usual  is  needed,  also, 
when  we  are  speaking,  in  order  to  keep  the  parts  properly  lubri- 
cated, for  the  passage  of  the  air  in  and  out  during  speaking 
dries  up  the  saliva  by  evaporation.  And,  accordingly,  the  mo- 
tion of  the  parts  at  such  times  stimulates  a  larger  flow,  just  as 
pressure  on  the  cheek  will  do  it,  as  before  remarked.  This 
result  is  favored  by  the  arrangement  of  the  duct  of  the  parotid 
gland,  which,  as  you  have  seen,  passes  over  one  large  muscle,  and 
then  through  the  body  of  another.  Chewing  any  thing  excites 


DIGESTION.  47 


Flow  of  saliva  affected  by  sympathy.     Swallowing. 


an  increased  flow  of  the  saliva ;  and  the  tobacco  chewer  does  a 
real  injury  to  the  salivary  glands,  by  keeping  them  constantly 
in  excessive  operation,  in  addition  to  the  ruinous  effects  of  this 
drug  on  the  system  at  larg'e.  When  he  eats,  these  over- worked 
factories  can  not  turn  out  as  good  an  article  as  they  should,  nor 
will  it  be  in  sufficient  quantity. 

76.  It  is  supposect  that,  besides  the  mere  mechanical  stimu- 
lus of  the  motion  of  the  parts,  the  stimulus  of  sympathy  is  also 
concerned  in  exciting  these  glands  to  increased  action.     The 
glands  are  supposed  to  be  affected  in  this  way  by  the  stimula- 
tion of  the  food  on  the  surface  of  the  mouth,  about  the  orifices  of 
their  ducts.     That  sympathy  does  have  an  influence  on  their 
secretion  is  evident  from  the  very  familiar  fact,  that  the  thought 
of  food  will  often,  as  it  is  expressed,  cause  the  mouth  to  water. 

77.  The  fact,  that  these  glands  do  not  all  secrete  the  same 
kind  of  fluid,  has  led  to  an  interesting  discovery  in  relation  to 
them.     The  submaxillary  glands  secrete  rather  a  viscid  fluid, 
while  that  which  is  poured  forth  by  the  parotid  and  sublingual 
glands  is  perfectly  limpid.     Now,  it  has  been  found,  by  various 
observations  and  experiments  on  animals,  that  while  the  teeth 
are  cutting  and  grinding  the  food,  and  the  parotid  and  sub- 
lingual  glands  are  pouring  out  the  saliva  to  moisten  it,  no  secre- 
tion comes  from  the  submaxillary  glands.     But  these  gland? 
pour  out  their  viscid  fluid  the  moment  that  the  tongue  thrusts 
the  food  back  towards  the  throat,  in  the  beginning  of  the  act 
of  swallowing.     The  special  object  of  this  viscid  fluid  is  then  to 
cover  the  food,  so  that  it  may,  to  use  a  common  expression,  slip 
down  easily  into  the  stomach ;  and  it  has  nothing  to  do  with 
the  moistening  of  the  food,  this  being  the  particular  office  of 
the  other  two  pairs  of  glands. 

78.  When  the   food   has  been  ground   by  the   teeth,   and 
moistened  by  the  saliva,  it  is  carried  by  the  act  of  swallowing 
into  the  stomach.     This  act,  simple  as  it  appears  to  you,  is  a 
very  complicated  one,  and  is  performed  by  the  conjoined  and 
agreeing  action  of  many  different  muscles.     The  food  is  first 
thrust  back  over  the  surface  of  the  tongue  into  the  large  cavity 
in  the  back  of  the  throat,  called  the  pharynx.     In  the  pharynx 
are  the  openings  of  two  tubes — the  oesophagus  or  gullet,  which 
is  the  passage  into  the  stomach,  and  the  trachea  *  or  windpipe, 
the  passage  to  the  lungs.      As  the  oesophagus  lies  behind  the 

*  This  term  is  sometimes  used,  as  here,  to  mean  the  whole  of  the  tube  conducting  to 
the  lungs,  including  the  larynx,  which  is  ut  the  top  of  this  tube,  and  sometimes  it  it 
eutricted  to  that  part  of  the  tube  which  is  below  the  larynx. 


48  HUMAN   PHYSIOLOGY. 

Parts  employed  in  swallowing.     Office  of  the  epiglottis. 

trachea,  the  food,  in  passing  to  it,  must  go  directly  over  the 
opening  into  the  trachea.  To  prevent  the  food  from  entering 
the  trachea,  therefore,  there  is  a  little  tongue -shaped  body, 
called  the  epiglottis,  extending  back  from  the  root  of  the  tongue, 
and  acting  as  a  lid  to  the  glottis,  the  opening  into  the  trachea. 
When  we  are  swallowing,  this  lid  is  shut  down  ;  but  it  is  always 
raised  up  when  we  are  breathing  or  speaking.  When  we  swal- 
low, not  only  does  the  lid  shut  down,  but  the  larynx  rises  to 
meet  the  lid,  as  you  may  readily  perceive,  if  you  place  your 
fingers  upon  what  is  called  Adam's  apple  while  you  are  swal- 
lowing. With  the  aid  of  Figures  10  and  11,  all  this  will  be 
very  clear  to  you.  In  Fig.  10,  you  have  -£  side  view  of  the 
parts  engaged  in  swallowing,  as  if  the  head  were  divided  into 
two  halves  by  a  vertical  section.  At  i,  is  the  cavity  of  the  nos- 
tril ;  at  A,  are  the  lips ;  a  is  the  divided  bone  of  the  chin ; 
b  is  the  tongue,  between  which  and  the  spinal  column,  /,  is  the 
large  cavity  of  the  pharynx.  In  front  of  this  cavity  hangs  the 


FIG.  10. 


f/ 


a-' 


e 

VERTICAL  SECTION  OF  THE  THROAT. 


palate,  <7,  as  a  door  or  valve,  to  direct  the  air  coming  from  the 
trachea,  d,  either  through  the  mouth  or  through  the  nostrils, 
according  to  its  position.  The  oesophagus,  e,  is  behind  the  tra- 
chea, and  the  epiglottis,  c,  shuts  down  when  we  swallow,  to  let 


DIGESTION. 


49 


Mode  of  action  of  the  oesophagus  in  swallowing. 


the  food  pass  over  it  into  the 
oesophagus.  In  Fig.  11,  you 
have  a  view  of  the  same  parts 
from  the  rear.  At  1,  is  a  sec- 
tion of  the  bones  at  the  base  of 
the  skull ;  3,  3,  are  the  cavities 
of  the  nostrils ;  2,  2,  the  walls 
of  the  pharynx  spread  apart ;  5, 
the  pendulous  palate ;  6,  6,  the 
arch  of  the  palate ;  8,  the  root 
of  the  tongue ;  9,  the  epiglottis, 
and  10,  the  glottis,  or  opening 
into  the  larynx;  13,  the  oeso- 
phagus; 14,  the  trachea.  The 
pharynx,  you  see,  is  a  funnel- 
shaped  cavity,  tapering  down  to 
the  oesophagus,  the  opening  of 
which  is  considerably  below  the 
opening  of  the  trachea. 

79.  When  the  food  enters  the 
oesophagus,  it  is  carried  through 

that  tube  into  the  stomach  by  the  ac- 
tion of  muscular  fibres.  These  fibres 
are  represented  in  Fig.  12.  The  cir- 
cular fibres  are  seen  at  a  and  b.  These 
are  removed  at  c,  so  as  to  show  the 
longitudinal  fibres.  It  is  by  the  con- 
sent of  action  between  these  different 
sets  of  fibres  that  the  food  is  propelled 
through  the  oesophagus.  As  the  food 
descends,  a  dilatation  of  the  circular 
fibres  must  everywhere  take  place 
where  the  food  is,  and  a  contraction 
of  them  immediately  behind  it — the 
dilatation  making  the  way  for  it,  and 
the  contraction  forcing  it  along.  And 
in  animals  that  chew  the  cud,  these 
actions  must  be  reversed  when  the  ball 
of  food  is  forced  up  through  the  esoph- 
agus into  the  mouth. 

80.  The  food  being  introduced  into 
the  stomach,  is  here  subjected  to  the 
action  of  the  gastric  juice.     This  is  a 

5 


FIG.  11. 


VIEW  OF  THE  THROAT  FROM 
BEHIND. 

FIG.  12. 


a 


CESOPHAGUS  LAID  OPEN. 


50  HUMAN   PHYSIOLOGY. 

Gastric  juice.     Chemical  in  its  action. 

peculiar  fluid,  somewhat  acid  in  its  character,  which  is  secreted 
by  very  minute  follicles,  or  bag-like  cavities,  situated  in  the  sub- 
stance of  the  mucous  membrane.  Ordinarily  there  is  none  of 
this  fluid  in  the  stomach  when  there  is  no  food  there.  Dr. 
Beaumont  made  some  very  interesting  observations  on  this,  as 
well  as  many  other  points,  in  the  remarkable  case  which  fell 
under  his  care.  The  individual,  Alexis  St.  Martin,  received  a 
wound  in  his  left  side  by  the  bursting  of  a  gun.  The  wound, 
which  opened  into  the  stomach,  never  entirely  closed,  but  an 
orifice  remained,  after  the  healing  process  had  done  all  that  it 
could.  Through  this  orifice,  Dr.  Beaumont  could  look  into  the 
stomach,  and  observe  what  was  going  on  there.  He  describes 
the  mucous  membrane,  in  its  healthy  state,  as  having  a  velvet- 
like  appearance,  with  a  pale  pink  color,  and  as  being  covered 
with  a  very  thin,  transparent,  viscid  mucus.  On  introducing 
some  food,  or  irritating  the  mucous  membrane  mechanically, 
he  saw,  by  the  aid  of  a  magnifying  glass,  "innumerable  lucid 
points  "  projecting  on  the  surface,  and  from  these  there  exuded 
a  pure,  limpid,  colorless  fluid.  These  points  were  the  follicles 
which  secrete  the  gastric  juice,  now  rendered  turgesceut  by 
being  stimulated  to  action. 

81.  The  amount  of  gastric  juice  secreted  is  generally  about 
in  proportion  to  the  amount  of  food  which  the  necessities  of  the 
system   require.     When   the   quantity  of  food  taken  is   very 
much   more   than  is    required,   there   can   not  be   a  sufficient 
amount  of  gastric  juice  secreted  to  digest  all  of  the  food  ;  anc 
some  of  the  food  must  therefore  remain  undigested,  and  will  prove 
a  source  of  irritation  to  the  stomach.     If  the  amount  of  food 
taken  from  day  to  day  is  not  very  excessive,  but  is  only  a  little 
above  the  proper  quantity,  there  will  be  enough  of  the  gastric 
juice  made  to  digest  it ;  but  the  daily  overtaxing  of  the  pow- 
ers of  the  secreting  follicles  will,  after  a  while,  produce  derange- 
ment in  the  stomach,  and  perhaps  permanent  disease. 

82.  The  action  of  the  gastric  juice  upon  the   food  is  of  a 
chemical  nature.     In   order  that  it  may  act  effectually  on  all 
portions  of  the  contents  of  the  stomach,  this  organ  is  kept  in 
constant  motion  by  the  fibres  of  its  muscular  coat.    These  fibres 
are  so  arranged  that,  as  they  contract  and  relax,  they  keep  up 
a  sort  of  churning  of  the  contents,  and  thus  effect  a  thorough 
mixture  of  them  with  the  gastric  juice.     In  Fig.  13,  you  see 
these  fibres  represented.     At  1,  is  the  opening  of  the  oesopha- 
gus into  the  stomach  ;  and  at  4,  is  the  part  which  opens  into 
the  intestine.     The  fibres  are  in  different  layers,  running  i« 


DIGESTION. 


51 


Churning  of  the  food  in  the  stomach.    The  chyme. 


FIG.  13. 


MUSCULAR  FIBRES  OF  THE  STOMACH. 


different  directions.  The  outer  peritoneal  coat,  5,  5,  is  dissected 
off  and  turned  back,  showing  some  of  the  fibres  that  run  length- 
wise of  the  organ,  6  ;  and  some  of  them  transverse,  7  ;  and 
others,  8,  that  run  obliquely.  You  can  readily  see  what  effect 
the  contraction  of  these  different  fibres  will  have  on  the  shape 
of  the  stomach.  The  contraction  of  the  longitudinal  fibres,  6, 
brings  the  large,  bulging  end  of  the  stomach,  2,  and  the  small 
end,  3,  nearer  together.  The  transverse  fibres,  when  they  con- 
tract, diminish  the  capacity  of  the  stomach  transversely.  And 
the  oblique  fibres  modify  these  two  motions  by  their  oblique 
action. 

83.  By  the  combined  chemical  and  mechanical  action  of  the 
stomach,  its  contents  are,  after  a  little  time — -in  three  or  four 
hours — reduced  to  an  uniform,  greyish,  semi-fluid  mass,  called 
chyme.  While  this  process  has  been  going  on,  the  communi- 
cation between  the  stomach  and  the  intestines  has  been  entirely 
closed  by  a  valve,  called  the  pylorus.  This  is  represented  at  5, 
in  Fig.  14,  which  presents  a  view  of  the  inside  of  the  stomach. 
This  valve  is  made  of  a  fold  of  both  the  mucous  and  muscular 
coats  of  the  stomach.  It  is  a  very  faithful  sentinel,  as  is  indi- 
cated by  its  name,  which  is  derived  from  two  Greek  words,  sig- 
nifying to  guard  the  gate.  It  wil-1  not  ordinarily  permit  any 
undigested  food  to  pass  it.  While  the  process  of  digestion  is 


52 


HUMAN  PHYSIOLOGY. 


The  pylorus.     A  sentinel.    On  duty  only  during  digestion. 


FIG.  14. 


INTERIOR  OF  THE  STOMACH  AND  SMALL  INTESTINE. 


going  on,  the  motions  produced  by  the  muscular  fibres  causa 
the  contents  to  move  about,  and  of  course  they  are  thrown 
against  the  pylorus,  as  well  as  any  other  part  of  the  stomach. 
But  the  valve  remains  closed,  until  some  portion  comes  against 
it  that  is  thoroughly  changed  to  chyme,  and  is  therefore  fit  to 
pass  on  into  the  intestine.  It  then  opens  to  let  this  pass,  and 
it  does  so  for  any  other  portions  that  have  become  chyme. 
Toward  the  conclusion  of  the  digestion  of  a  meal,  small  quan- 
tities pass  at  first,  and  after  a  while,  the  contents  pass  quite 
rapidly  through  the  valve. 

84.  Although  this  sentinel-valve  thus  performs  its  duty  so 
faithfully  in  relation  to  nutritive  substances,  it  seems  to  let  other 
substances  pass  very  readily.  Solid  substances,  swallowed  by 
mistake,  as  buttons,  pieces  of  money,  the  pits  and  skins  of  vari- 
ous fruits,  often  pass  the  valve  without  any  trouble.  The  vaive 
seems  to  be  on  duty  as  a  sentinel  only  during  the  process  of 
digestion ;  and,  if  the  attempt  to  go  through  with  this  process 
prove  unavailing,  the  pylorus,  though  it  let  such  hard  sub- 
stances as  I  have  mentioned  pass  without  difficulty,  resists  the 
passage  of  the  undigested  food,  sometimes  causing  much  un- 
easiness, and  even  perhaps  pain,  by  so  doing.  In  such  a  case, 
either  the  valve  after  a  time  gives  over  its  resistance,  or,  hold- 


DIGESTION.  53 


Theories  of  digestion.    Eating  between  meals.    Eating  fast. 

ing  out,  the  action  of  the  stomach  is  reversed,  and  the  offending 
matter  is  thrown  off  by  vomiting. 

85.  It  is  not  a  little  amusing  to  read  the  different  theories 
which  were  formerly  broached  to  explain  the  process  of  diges- 
tion.    Some  supposed  it  to  be  a  concoction,  heat  being,  in  their 
view,  the  chief  agent ;  some,  a  kind  of  putrefaction ;  some,  a 
chemical  solution;  some,  a  trituration ;  and  some,  a  process 
dependent  upon  the  action  of  the  nerves.     Of  these  various 
theories,  the  celebrated  Hunter  playfully  remarked:  "To  ac- 
count for  digestion,  some  have  made  the  stomach  a  mill ;  some 
would  have  it  to  be  a  stewing-pot,  and  some,  a  brewing-trough ; 
yet,  all  the  while,  one  would  have  thought  that  it  must  have 
been  very  evident  that  the  stomach  was  neither  a  mill,  nor  a 
stewing-pot.  nor  a  brewing-trough,  nor  any  thing  but  a  sto- 
mach"    All  these  theories  are  now  done  with ;  and  it  is  pretty 
well  ascertained,  that  digestion  is  a  chemical  process — in  part  a 
solution,   and   in   part  a   fermentation — and   that   mechanical 
agency  is  employed  only  for  the  purpose  of  thoroughly  exposing 
the  food  to  the  action  of  the  gastric  juice. 

86.  The  process  of  digestion,  as  it  has  been  described,  is  a 
regular  process,  requiring  a  certain  average  period  of  time  for 
its  completion.     If,  during  the  progress  of  it,  fresh  food  be  in- 
troduced, its  regularity  is  broken  in  upon,  and  the  process  fails 
to  be  well  done.    Then,  too,  if,  immediately  after  the  completion 
of  the  process,  a  new  supply  of  food  be  taken,  harm  is  done, 
because  the  organ  has  not  its  needed  interval  of  rest.     For 
these  reasons,  the  practice  of  eating  between  meals  is  a  very 
injurious  one.     Eating  fast  does  harm,  because, — 1st,  the  food  is 
not  sufficiently  ground  ;  2d,  it  is  not  mixed  thoroughly  with  the 
saliva ;  and,  3d,  more  food  is  taken  than  would  be  sufficient  to 
satisfy  the  hunger  if  the  individual  ate  slowly,  and,  therefore, 
more  than  can  be  easily  digested.     Great  variety  in  food  stimu- 
lates the  appetite  unduly,  and  too  much  is  consequently  eaten. 
Exercise  facilitates  digestion,  if  it  be  not  violent.     An  experi- 
ment was  once  tried  upon  two  dogs,  which  was  thought  to 
prove  that  exercise  hindered  digestion.     Two  dogs  were  fed 
freely,  and  while  one  was  left  to  lie  still,  the  other  was  made  to 
run  about  violently.     Both  dogs  were  kiPed  after  an  hour  or 
two,  and  it  was  found  that,  while  digestion  had  gone  on  thor- 
oughly in  the  dog  that  was  allowed  to  remain  quiet,  in  the 
other  the  food  was  undigested.     This  only  proved  that  violent 
exercise,  taken  immediately  after  eating,  impedes  digestion.     It 
has  been  found,  on  the  other  hand,  that  light  exercise  pro- 

5* 


64  HUMAN   PHYSIOLOGY. 

Cause  of  hunger,  state  of  the  system.    Its  seat  in  the  stomach. 

motes  the  process ;  and  daily  experience,  among  laborers,  shows, 
that  very  strong  exercise  does  not  interfere  with  it,  if  a  little 
interval  of  rest  be  allowed,  so  that  the  process  may  be  fairly 
begun. 

87.  The  sensation  of  hunger  has  been  attributed  to  various 
causes, — as  the  empty  state  of  the  stomach,  the  presence  of  the 
gastric  juice  irritating  the  mucous  membrane,  &c.  It  cannot 
arise  from  emptiness ;  for,  if  it  were  so,  it  should  occur  sooner 
than  it  does  after  eating,  and  it  should  not  be  absent  in  dis- 
ease, as  it  often  is  for  a  long  time,  when  the  stomach  is  almost 
entirely  empty.  It  can  not  arise  from  the  irritation  of  the  gas- 
tric juice ;  for  it  was  found  by  Dr.  Beaumont,  in  his  observa- 
tions of  the  stomach  of  Alexis  St.  Martin,  that  this  fluid  is  not 
secreted  till  after  food  is  introduced  into  the  stomach.  The 
cause  of  hunger  is  evidently  in  the  state  of  the  system.  It  is 
a  state  of  want.  Nutriment  is  needed  by  the  formative  vessels, 
the  builders  and  repairers  of  the  system,  of  which  I  shall  speak 
particularly  in  the  chapter  on  Formation  and  Repair.  And 
they  make  their  wants  known  as  distinctly  as  the  bricklayer 
does,  when  he  calls  for  more  brick  and  mortar.  Through  the 
nerves,  an  impression  is  communicated  from  these  to  the  sto- 
mach, and  the  sensation  of  hunger  is  the  result.  That  the  sen- 
sation is  seated  there  is  evident  from  the  fact,  that  it  can  be 
temporarily  relieved  by  putting  indigestible  substances  into  the 
stomach.  These  produce  the  effect  by  causing  other  sensations 
there,  which  take  the  place,  for  the  time  being,  of  the  sensation 
of  hunger.  After,  however,  the  momentary  effect  is  over,  the 
sensation  of  hunger  returns  again  in  its  full  force.  The  cause, 
then,  of  the  sensation  is  in  the  system  at  large,  but  its  seat  is 
in  the  stomach.  Its  degree  of  urgency  depends  upon  this 
general  state  that  causes  it.  If  eating  be  delayed  ranch  beyond 
its  usual  time,  or  if  the  system  has  been  exhausted  by  the  wear 
and  tear  of  severe  labor,  the  sensation  of  hunger  is  very  urgent. 
So,  too,  if  disease  has  impoverished  the  system,  as  soon  as  the 
stomach  is  in  a  condition  to  respond  to  the  call  of  the  forma- 
tive vessels  that  set  themselves  to  work  to  repair  the  waste,  the 
hunger  is  often  excessive.  Observe,  here,  that  in  order  to  have 
the  sensation  of  hunger,  not**bnly  must  there  be  a  want  in 
the  system  at  large,  but  the  stomach  must  be  in  a  state  fitted 
to  receive  the  notice  of  this  want.  And  fortunately  it  is  seldom 
in  this  state  except  when  in  a  condition  to  do  its  work.  If  it 
were  otherwise,  food  would  often  be  introduced  into  it  when  it 
could  not  be  digested.  The  stomach  is  sometimes  incapacitated 


DIGESTION.  55 


Sensation  of  hunger  affected  by  the  mind.    Thirst. 


for  receiving  the  notice  of  the  want  of  the  system  by  mental 
impressions.  In  this  case,  an  impression  is  communicated  from 
the  brain  to  the  stomach,  through  the  nerves,  which  counteracts 
the  impression  conveyed  from  the  system  to  this  organ,  and  so 
neutralizes  the  sensation  of  hunger.  Grief  tfcus  often  destroys 
the  appetite  for  food.  One  thing  more  is  to  be  observed  in 
relation  to  hunger.  Although  this  sensation  is  caused  by  the 
want  of  the  system,  it  is  removed  long  before  the  nutriment 
reaches  its  final  destination,  and  supplies  the  want.  How  is 
this  ?  It  is  either  because  the  new  sensations  produced  in  the 
stomach,  by  the  commencing  process  of  digestion,  take  the 
place  of  the  sensation  of  hunger,  or  an  impression  is  sent  all 
over  the  system  from  the  filled  stomach,  which,  so  to  speak,  stills 
the  clamor  of  want  with  the  immediate  prospect  of  a  supply. 

88.  Nearly  the  same  remarks  can  be  made  in  relation  to 
thirst,  that  have  been  made  in  regard  to  hunger.     The  seat  of 
this  sensation  is  in  the  fauces  or  throat.     Its  cause  is  evidently 
not  there ;  for  the  mouth  and  throat  may  be  very  dry,  and  yet 
there  may  be  little  or  no  thirst;  while,  on  the  other  hand,  there 
may  be  much  thirst,  although  the  mouth  and  throat  are  moist. 
The  cause  of  the  sensation  is  like  the  cause  of  hunger,  in  the 
system  at  large ;  and,  therefore,  no  local  cause,  producing  a 
dryness  of  the  throat,  can  cause  thirst  independent  of  a  general 
condition. 

89.  Before  describing  the  remainder  of  the  process  of  diges- 
tion, I  will  call  your  attention  to  the  arrangement  of  the  sto- 
mach, and  the  other  organs  of  the  abdomen  engaged  in  this 
process.     Fig.  15  exhibits  them  as  they  present  themselves  in 
a  front  view,  except  that  they  are  somewhat  separated  from 
each  other,  instead  of  being  as  closely  packed,  as  they  are  in  the 
abdomen.     The  large  end  of  the  stomach,  you  see,  lies  to  the 
left  side,*  and  at  this  end  is  the  spleen.     The  pancreas  is  be- 
hind the  right  end  of  the  stomach.     Above  the  stomach,  and 
mostly  to  the  right  side,  is  the  largest  organ  in  the  abdomen, 
the  liver.     It  is  represented  as  turned  upward  in  the  Figure. 
The  stomach  is  directly  connected  with  the  small  intestines  at 
the  pylorus.     At  the  end  of  this  long  and  winding  tract  begin 
the  large  intestines.     The  duct  of  the  gall  bladder,  and  that  of 
the  pancreas,  empty  their  contents  into  the  small  intestine  at  its 
beginning.     The  office  of  the  spleen  has  not  yet  been  ascer- 
tained.    Neither  has  that  of  the  worm-like  appendage  at  the 

*  As  this  is  a  front  view,  the  right  side  of  the  Figure  is  the  left  side  of  the  body. 


56 


HUMAN   PHYSIOLOGY. 


Arrangement  of  the  digestive  organs. 


FIG.  15. 


GALL  BLADDER.' 


LARGE  INTES— - 
TINES. 

BEGINNING  OF 
LARGE    IN- 
TESTINES. 

WORM-LIKE  AP- 
PENDAGE. 


-SPLEEN. 


LARGE  INTES- 
TINES. 


SMALL  INTES- 
TINES. 


8MALL  INTESTINES. 

DIGESTIVE  ORGANS. 

beginning  of  the  large  intestines.  The  omentum,  or  caul, 
which  hangs  like  a  curtain  from  the  front  part  of  the  sto- 
mach down  in  front  of  the  intestines,  is  not  represented  in  the 
Figure. 

90.  There  is  one  arrangement  in  the  abdomen  which  must 
not  pass  unnoticed.  If  the  intestines  were  left  to  lie  loose  in 
this  cavity,  they  would  constantly  be  subject  to  displacement 
and  injury.  They  are  therefore  fastened  to  the  backbone  by 
an  arrangement,  which  secures  them  from  any  such  accident, 
and  at  the  same  time  allows  of  a  sufficiently  free  motion  of  differ- 


DIGESTION.  57 


The  arrangement  of  the  mesentery.    Its  offices. 


ent  parts  of  this  tube.  It  is  this.  The  intestinal  tube  makes 
the  margin  of  a  broad  sheet  of  membrane,  the  other  edge  of 
which  is  gathered  up  and  fastened  to  the  spinal  column.  The 
arrangement  is  like  a  ruffle  with  a  puffed  edging.  The  mem- 
branous sheet  is  called  the  mesentery.  As  the  intestinal  tube, 
the  puffed  edging,  is  much  longer  than  the  ruffle  itself,  the 
mesentery,  it  is  gathered  on  to  the  ruffle,  as  a  seamstress  would 
express  it.  Now,  the  mesentery  is  composed  of  two  folds  of 
the  peritoneum,  the  smooth,  shining,  outer  covering  of  the  in- 
testines. The  arrangement  will  be  easily  understood  by  the 
diagram  in  Fig.  16,  which  represents  a  section  of  the  intestine 
with  the  mesentery.  The  cav- 
ity of  the  intestine,  a,  is  lined  FIG.  16. 
by  the  mucous  membrane  re- 
presented by  the  inner  circle. 
Next  comes  the  muscular  coat, 
and  next  the  peritoneal,  the 
outer,  which,  instead  of  making 
a  circular  tube,  as  the  other  two 
coats  do,  passes  backward  on 
both  sides  of  the  intestine,  to 
make  the  mesentery,  b.  After  • 
being  attached  to  the  spine  by  PLAN  OF  THE  MESENTERY. 
means  of  cellular  tissue,  it  is  re- 
flected off  to  pass  over  other  portions  of  the  intestine,  as  seen  at 
c,  c.  Between  the  two  layers  of  the  peritoneal  membrane,  in  the 
mesentery,  is  considerable  space,  as  seen  at  b.  This  space  is 
rilled  up  with  blood-vessels,  nerves,  lacteals  with  their  small 
glands,  soon  to  be  described,  all  bound  together  by  the  com- 
mon packing  material  of  the  body,  the  cellular  tissue.  You 
see,  therefore,  that  the  mesentery  subserves  more  than  one  use. 
Besides  fastening  the  whole  tract  of  the  intestinal  canal  to  the 
spine,  so  as  to  guard  it  against  accident,  it  acts  as  a  secure 
medium  for  the  communication  of  the  blood-vessels  and  nerves 
with  the  intestines.  And,  besides,  as  you  will  soon  see,  it  con- 
tains the  little  tubes  which  convey  all  the  nutriment  into  the 
blood  for  the  growth  and  repair  of  the  body. 

91.  I  now  go  on  to  describe  the  remainder  of  the  process  of 
digestion.  The  chyme,  (§  83,)  as  it  passes  into  the  small  intes- 
tine from  the  stomach,  has  mingled  with  it  the  -bile-~and  the 
secretion  of  the  pancreas.-  These  are  poured  into  the  intestine 
at  the  point  represented  at  6,  in  Fig.  14.  These  secretions  un- 
doubtedly have  some  agency  in  separating  the  nutritious  part 


58 


HUMAN   PHYSIOLOGY. 


Chyme.    Chyle.    Lacteals.    Thoracic  duct. 


of  the  chyme  from  that  which  is  not  so.  When  thus  separat- 
ed, it  is  absorbed  by  the  innumerable  small  vessels,  called  lac- 
teals,  which  are  situated  in  the  mucous  membrane.  This  nutri- 
tious part  of  the  chyme  is  a  milky  fluid,  called  the  chyle.  The 
lacteals  which  absorb  it  are  little  tubes  or  ducts.  These  enter 
certain  glands,  called  the  mesenteric  glands,  for  the  purpose  of 
having  some  effect,  we  know  not  what,  produced  upon  it.  They 
then  pass  on,  as  seen  in  Fig.  17,  to  pour  their  contents  into  the 


*•>'    ORIGINS 
OP 

LACTEALS. 


SECTION  OF  INTESTINE  SHOWING  THE  LACTEALS. 


thoracic  duct.  This  duct,  which  is  about  the  size  of  a  common 
quill,  running  up  on  the  left  side  of  the  aorta,  the  great  artery 
of  the  heart,  pours  its  contents  into  the  junction  of  two  veins 
at  the  top  of  the  chest.  As  the  circulation  of  the  chyle  in  the 


DIGESTION.  59 


Mechanical  contrivance  of  the  thoracic  duct.     Chyle  makes  blood. 


thoracic  duct  needs  all  the  mechanical  help  that  it  can  have,  the 
mode  of  the  joining  of  this  duct  with  these  veins  is  calculated 
to  facilitate  the  freeness  of  the  discharge  of  the  chyle.  As 
the  two  large  currents  in  the  veins,  v  and  v,  v,  in  Fig.  18, 


FIG.  18. 


JUNCTION  OF  THE  THORACIC  DUCT  WITH  THE  VEINS. 

unite,  there  is  created,  by  the  forward  motion  of  these  cur- 
rents, a  tendency  to  a  vacuum  at  the  angle  at  which  they 
meet,  the  point  where  the  thoracic  duct,  T,  D,  opens.  There 
is,  therefore,  a  suction  power,  as  it  is  termed,  exerted  upon 
the  fluid  in  this  duct.  The  chyle,  thus  mingled  with  the 
blood,  becomes  a  part  of  it.  Or  rather,  I  should  say,  that  the 
blood  is  made  from  the  chyle,  and,  as  it  is  constantly  used  for 
formation  and  repair  in  all  parts  of  the  system,  it  is  thus  as 
constantly  replenished.  The  material  by  which  all  the  textures 
of  the  body  are  made  and  are  kept  in  repair,  is  furnished  to 
the  system  through  this  small  duct,  in  the  form  of  a  milky 
fluid.  You  observe  in  Fig.  17,  certain  lymphatic  vessels.  These 
are  trunks  of  absorbents,  hereafter  to  be  spoken  of  particularly, 
which  bring  a  fluid  called  lymph,  to  be  mingled  with  the  chyle, 
and  to  be  poured  with  it  into  the  circulation. 

92.  The  extent  of  surface  on  which  the  absorbent  lacteals 
open  can  not  be  appreciated,  if  you  look  merely  at  the  outside 
of  the  small  intestines.  It  can  be  done  only  by  looking  at  the 
inner  mucous  coat.  This  coat  is  really  much  more  extensive 
than  the  outer  coat,  or  the  middle  one,  the  muscular,  arid  it  is 
full  of  folds,  as  represented  in  Fig.  14,  on  page  52.  The  ob- 


60  HUMAN  PHYSIOLOGY. 

Extent  of  absorbing  surface  in  intestines.    Alimentary  canal  in  different  animals. 

ject  of  this  is  to  offer  a  very  large  absorbing  surface  to  the 
chyme  as  it  passes,  and  also  to  prevent  its  passing  along  as 
rapidly  as  it  would  if  the  mucous  surface  were  perfectly  smooth, 
instead  of  having  folds.  Before  leaving  this  subject,  I  would 
again  call  your  attention  to  the  analogy  which  exists  between 
absorption  in  animals  and  in  plants.  The  lacteals  do  for  the 
animal  in  its  stomach,  what  the  absorbents  do  for  the  plant  in 
the  extremities  of  its  roots.  Both  absorb  and  assimilate  nutri- 
ment. The  function  is  the  same.  It  differs  in  the  two  cases 
only  in  the  circumstances  under  which  it  is  performed. 

93.  The  digestive  apparatus  varies  much  in  different  animals, 
according  to  the  kinds  of  food  on  which  they  live.     As  a  gene- 
ral rule,  the  more  the  food  differs  in  character  from  the  animal 
itself,  the  more  complicated  and  extensive  is  the  apparatus. 
Thus,  the  herbivorous  animals  have  a  very  long  alimentary 
canal,  and  the  beginning  of  it,  the  stomach,  is  a  complicated 
organ.     While,  on  the  other  hand,  in  the  carnivorous,  the  flesh 
which  they  eat  being  very  much  like  their  own  flesh,  and,  there- 
fore, not  requiring  very  much  of  a  process  of  assimilation,  the 
stomach  is  a  simple  organ,  and  the  alimentary  canal  is  very 
short.    In  the  sheep,  for  example,  the  alimentary  canal  is  about, 
twenty-eight  times  the  length  of  the  body,  but  in  the  lion  it  is 
only  three  times  its  length.     In  man,  who  lives  on   a  mixed 
diet,  the  alimentary  canal  is  about  six  times  the  length  of  the 
body. 

94.  The  stomach  is  more  complicated  in  animals  that  chew 
the  cud  than  in  any  other  animals.    It  has  four  distinct  cavities, 
and,  as  you  will  see,  a  singular  mechanism  is  called  into  opera- 
tion in  managing  the  food  as  it  passes  through  them.     In  Fig. 
19,  you  have  a  representation  of  the  stomachs  of  the  sheep,  as 
they  appear  exteriorly.     The  course  which  the  food  pursues  is 
this.     As  the  animal  crops  the  food,  it  passes  into  the  first  sto- 
mach, which  is  little  else  than  a  great  reservoir  to  hold  it  and 
to  soak  it.     Then  it  passes  into  the  second  stomach,  from  which 
it  is  returned  into  the  mouth.     On  being  swallowed  again,  it 
passes  from  the  oesophagus  into  the  third,  and  thence  into  the 
fourth  stomach.     In  Fig.  20,  you  see  the  interior  of  these  four 
stomachs ;  and  by  the  aid  of  this  I  will  describe  the  process  of 
digestion  in  the  sheep  more  particularly.     You  see  the  very 
large  first  stomach,  or  paunch,  in  which   the   food  is  accumu- 
lated.    It  is  not  yet  masticated  thoroughly,  for  the  animal  has 
swallowed  it  as  fast  as  he  could,  and  packed  it  away  in  this 
reservoir.     From  this  it  is  passed,  in  small  quantities  at  a  time, 


DIGESTION". 


Digestion  in  the  sheep. 


OESOPHAGUS. 


ORIFICE  OF 
STOMACH. 

3D  STOMACH. 


FIG.  19. 


STOMACHS  OF  THE  SHEEP. 


FIG.  20. 


INTERIOR  OF  THE  STOMACHS  OF  THE  SHEEP. 


into  the  second  stomach,  the  honey-comb,  so  called  from  the 
peculiar  network  of  folds  in  it.  Here  the  food  is  rolled  up  into 
balls  by  the  action  of  the  muscular  fibres  in  this  network. 

6 


62  HUMAN  PHYSIOLOGY. 

Digestive  apparatus  in  birds.    Different  in  the  grain-eating  and  the  flesh-eating. 

Each  ball  of  food  is  passed  up  through  the  oesophagus  into  the 
mouth,  where  it  is  chewed  and  thoroughly  mixed  with  the  saliva, 
in  doing  which  the  animal  seems  to  have  great  enjoyment. 
Then  it  is  swallowed,  and,  as  it  passes  from  the  oesophagus,  in- 
stead of  going  into  the  paunch,  as  it  did  when  swallowed  the 
fhst  time,  it  is  directed  through  the  groove  seen  in  the  Figure 
into  the  third  stomach,  the  manyplies.  This  has  many  folds, 
like  the  leaves  of  a  book,  so  that  the  food  is  exposed  to  a  large 
surface  in  this  cavity.  It  passes  from  this  to  the  fourth  sto- 
mach, the  reed.  Here,  and  here  only,  it  is  acted  upon  by  the 
gastric  juice.  This,  therefore,  is  the  true  stomach,  all  the  other 
cavities  furnishing  only  preparatory  steps  to  the  true  process  of 
digestion.  It  is  from  this  fourth  stomach  that  what  is  called 
the  rennet  is  taken.  When  fluid  matter  is  swallowed,  it  goes 
directly  into  the  second  stomach,  and  not  into  the  first,  the 
paunch ;  so  that,  in  the  case  of  the  sheep,  the  drink  goes  one 
way,  and  the  solid  food  another.  And,  what  is  still  more  singu- 
lar, while  the  animal  is  a  suckling,  the  milk  passes  directly  into 
the  fourth  stomach  through  the  third,  which  has  its  folds  so 
closed  together  as  to  form  a  mere  tube  to  conduct  it  to  its  des- 
tination. And  the  great  paunch  and  the  honey-comb  are 
wholly  useless  until  the  animal  begins  to  crop  its  food  for 
itself. 

95.  In    birds,  the   digestive    apparatus   is   necessarily  very 
peculiar,  from  the  fact  that  they  do  not  masticate  their  food. 
They  have,  on  this  account,  an  arrangement  in  the  stomach 
itself  for  grinding  the  food.     In  the  cavity  called  the  gizzard 
are  two  opposing  surfaces,  made   very  hard,  so  that  by  rub- 
bing together  they  bruise  the  grains ;    and    while   they  are 
thus   ground,   as    between    two    millstones,    the   gastric  juice 
is  poured  down  upon  them  from  above.     This  arrangement  is 
seen  in  Fig.  21,  which  represents  the  digestive  apparatus  in  the 
turkey  laid  open.     At  b  is  the  gizzard,  showing  the  two  hard 
surfaces,  which  are  rubbed  together  by  the  stout  muscles  that 
make  the  great  bulk  of  the  organ.      Above,  at  a,   are  the 
glands  which   pour  forth  the  gastric  juice.     And  above  this 
part  of  the  stomach  there  is,  in  all  grain-eating  birds,  a  large 
sac  bulging  out  from  the  oesophagus,  called  the  crop,  which  is 
a  reservoir  for  the  food,  just  as  the  paunch  is  in  the  ruminating 
animals.     In  those  birds  that  live  on  flesh  or  fish  there  is  no 
such  grinding  apparatus;  and  the  walls  of  the  stomach  are 
quite  thin,  and  it  presents  no  hard  surfaces. 

96.  It  would  be  interesting,  were  it  consistent  with  the  plau 


DIGESTION. 


63 


Pigestion  in  the  turkey.     Digestive  apparatus  in  different  animals. 


FIG.  21. 


STOMACH  OF  THE  TURKEY. 


of  this  book,  to  go  into  a  further  examination  of  the  varieties 
in  the  digestive  apparatus  in  different  animals.  They  have  a 
very  wide  range,  being  according  to  the  wants  of  the  animal  in 
each  case.  The  kind  of  food,  the  mode  of  life,  and  the  pur- 
pose which  the  animal  is  designed  to  fulfill,  are  the  circumstances 
which  govern  these  variations.  The  proportion  which  the  di- 
gestive apparatus  bears  to  other  parts  varies  very  much ;  and 
in  some  of  the  lower  orders  of  animals,  the  body  seems  to  be 
all  stomach.  In  such  cases,  the  only  appendages  are  those  which 
seize  the  food  and  direct  it  into  the  orifice  of  this  organ.  This 


64  HUMAN  PHYSIOLOGY. 

Apparatus  of  the  circulation.    Heart,  arteries,  veins,  capillaries. 

is  the  case  with  the  hydra,  represented  in  Fig.  1.  And,  what 
is  very  singular,  the  outside  of  the  body  of  this  animal  is  just 
as  capable  of  acting  as  a  stomach  as  its  inside.  For  you  may 
turn  it  inside  out,  as  you  can  a  stocking,  and  yet  it  will  go  on 
to  catch  and  digest  its  food  as  usual.  But,  wide  as  the  varia- 
tions are  in  the  digestive  apparatus  of  animals,  the  same  com- 
mon object  is  aimed  at  in  all — the  assimilation  (§  10)  of  nu- 
trient substances  to  the  animal,  to  produce  a  material  from 
which  its  structure  can  be  built  and  kept  in  repair.  There  is, 
therefore,  much  that  is  common  to  them  all  in  the  modes  in 
which  this  object  is  accomplished.  And  even  the  analogy 
which  exists  between  the  animal  and  plant,  in  regard  to  assimi- 
lation, does  not  relate  to  the  fact  alone,  but  in  some  measure  to 
the  modes  in  which  the  process  is  effected. 


CHAPTER  VI. 

CIRCULATION  OF  THE  BLOOD. 

97.  IN  the  last  chapter  I  described  the  manner  in  which  the 
blood  is  made  from  the  food.     The  blood,  thus  prepared,  is 
circulated  in  every  part  of  the  body,  that  it  may  be  used  for 
the  purposes  of  construction  and  repair.     The  apparatus  by 
which  this  is  done  acts,  as  I  have  before  said,  as  the  common 
carrier  of  the  material  which  is  used  everywhere  in  the  body 
by  the  laborers,  the  builders,  to  whom  it  is  thus  brought. 

98.  This  apparatus  consists  of  several  parts — a  great  central 
organ,  the  heart,  situated  in  the  chest;  the  arteries,  the  tubes 
by  which  the  blood  is  conducted  to  all  parts  of  the  body ;  the 
veins,  other  tubes,  which  bring  the  blood  back  to  the  heart ; 
and  capillaries,  a  network  of  exceedingly  minute  vessels,  through 
which  the  blood  passes  as  it  goes  from  the  extreme  arteries  into 
the  beginnings  of  the  veins.      The  blood  goes  from  the  heart 
through   a  large   artery,  called  the  aorta,  which  sends  forth 
branches ;  and  these  divide  and  subdivide,  so  that  the  extreme 
arteries,  through  which  the  blood  flows  into  the  capillary  net- 
work, are  very  minute.     And  the  veins  which  receive  the  blood 
from  this  network  to  carry  it  back  to  the  heart,  are  equally 
minute ;  but  joining  together  more  and  more,  as  they  proceed 


THE   CIRCULATION.  b'5 


Heart  n  forcing  and  suction  pump.     Arteries  firm  tubes.     Why. 

toward  the  heart,  they  are  at  length  all  united  into  two  great 
venous  trunks,  one  from  above  and  the  other  from  below,  which 
pour  their  contents  into  this  organ.  The  capillaries,  taking 
their  namev  from  the  Latin  word,  capilla,  a  hair,  are  so  small 
that  the)7"  can  not  be  seen  by  the  naked  eye.  In  any  small 
cut,  the  blood  which  oozes  out  comes  from  multitudes  of  these 
vessels.  They  serve  to  hold  the  blood,  while  the  formative  ves- 
sels, that  construct  and  repair  the  body,  may  select  from  it  such 
materials  as  they  need  for  their  purposes. 

99.  The  heart  is  a  great  central  forcing  and  suction  pump,  in 
the  midst  of  this  circulating  apparatus.     When  it  contracts,  it 
forces  the  blood  out  through  the  aorta  and  its  branching  ar- 
teries into  all  parts  of  the  system.      And  when  it  enlarges  or 
dilates  itself,  it,  by  suction,  as  it  is  termed,  receives  the  blood 
returning  from  the  system  through  the  veins.    The  blood  never 
ceases  to  go  these  rounds.     The  necessity  for  this  continual 
motion  you  will  perceive  as  I  proceed  with  the  development  of 
the  subject.  • 

100.  The  arteries  differ  from  the  veins  in  their  structure  and 
arrangement.     The  arteries  are  firm  tubes,  while  the  veins  are 
lax  in  their  structure.     The  object  of  the  difference  is  obvious. 
As  the  blood  is  forced  into  the  arteries  by  the  powerful  action 
of  the  heart,  it  is  necessary  that  they  should  be  strong  and 
firm,  else,  they  would  be  liable  to  dilatation  and  rupture,  and 
death  would  frequently  result.     As  it  is,  it  is  not  a  common 
event  to  have  an  artery  dilate  and  burst,  though  it  does  occa- 
sionally happen.     When  dilatation  does  occur  in  an  artery,  it 
is  called  an  aneurism.     But  the  arteries  need  to  be  firm,  not 
only  for  the  sake  of  security  against  rupture,  but  also  that  the 
force  of  the  heart  may  propel  the  blood  to  the  extremities  of 
the  arterial  system.     If  the  arteries  were  lax  tubes,  like  the 
veins,  the  impulse  would  soon  be  lost  in  the  yielding  tubes,  and 
the  blood  would  move  very  sluggishly  in  the  small  arteries  at  a 
distance  from  the  heart.     What  we  call  the  pulse,  is  caused  by 
this  impulse.     If  the  arteries  were  lax  tubes,  the  pulse  would 
not  be  felt  at  any  great  distance  from  the  heart.      Instead  of 
being  distinct,  as  it  now  is,  w^h  every  beat  of  the  heart  almost 
to  the  very  extremities  of  the  arterial  system,  it  would  be  ren- 
dered confused  by  the  yielding  of  the  tubes,  even  quite  near 
the  heart,  and  at  a  distance  from  that  organ  it  would  be  en- 
tirely lost. 

101.  Besides  the  firmness  of  the  arteries,  there  is  another 
circumstance  which  favors  the  freeness  of  the  flow  of  blood 

6* 


66  HUMAN   PHYSIOLOGY. 

Different  arrangement  of  arteries  and  veins. 

through  them.  It  is  their  mode  of  division.  The  branch  of 
an  artery  leaves  the  main  trunk  at  a  sharp  angle,  making  thus 
only  a  slight  deviation  from  the  direction  of  the  current ;  while, 
on  the  other  hand,  in  the  veins  where  the  current  flows  in  an 
opposite  direction,  the  branch  unites  with  the  trunk  at  nearly  a 
right  angle.  This  difference  is  represented  in  Fig.  22  ;  1  being 
the  artery,  and  2  the  vein. 

FIG.  22. 


ARTERY  AND  VEIN. 

102.  The  venous  system  has  a  much  greater  capacity  than 
the  arterial.  That  is,  all  the  veins  of  the  body  are  together  ca- 
pable of  holding  more  blood  than  all  the  arteries  are.  And  the 
blood  moves  very  rapidly  and  directly  from  the  heart  through 
the  arteries,  but  it  conies  back  to  the  heart  quite  slowly  through 
the  veins.  Every  thing  is  arranged  to  promote  this  rapid  cir- 
culation through  the  arteries,  while  the  venous  system  is  calcu- 
lated for  a  slow  but  sure  progress  of  the  blood  back  to  the 
heart.  To  secure  this,  valves,  made  of  folds  of  the  inner  lining 
of  the  veins  are  so  arranged  as  to  prevent  the  blood  from  flow- 
ing in  the  wrong  direction.  Fig.  23  represents  a  vein  cut  open 
so  as  to  show  these  valves.  A  shows  the  valves  as  they  appear 
when  the  vein  is  laid  open  and  spread  out ;  B,  as  they  appear 
when  the  vein  is  simply  laid  open ;  and  C  represents  the  ap- 
pearance of  the  outside  of  the  vein  where  there  are  valves. 


THE   CIKCULATION. 


67 


Valves  in  veins.    Dangerous  to  wound  an  artery.    Therefore  well  guarded 


VALVES  IN  THE  VEINS. 


The  need  which  there  is  of  this  help  to  the  circulation  through 
the  veins  is  obvious.  The  suction  power  of  the  heart  is  not 
competent,  unaided,  to  move  the  blood  throughout  all  the  lax 
venous  system.  These  pocket-like  valves,  therefore,  are  made 
in  the  veins  to  assist  the  circulation  there.  They  do  so  in  this 
way.  Every  motion  of  the  muscles  or  other  parts  about  the 
veins  tends  to  keep  the  blood  in  motion,  and  the  valves  serve  to 
prevent  this  motion  from  being  in  the  wrong  direction.  The 
difference  in  force  and  velocity  with  which  the  blood  moves  in 
the  arteries  and  in  the  veins,  is  made  manifest  when  they  are 
wounded.  The  blood  flows  from  a  wounded  vein  in  a  slow 
and  steady  stream.  From  an  artery  it  flows  rapidly,  showing 
the  impulse  of  the  heart  in  its  jets,  which  correspond  exactly 
with  the  pulse.  Hence  comes  the  danger  in  wounding  an  ar- 
tery, while  the  wound  of  a  vein  is  ordinarily  attended  with  no 
danger.  Accordingly,  we  find  that  the  "Maker  of  our  bodies" 
has  so  placed  the  arteries  that  they  cannot  easily  be  wounded, 
while  many  of  the  veins  are  quite  freely  exposed.  The  arteries 
are  deeply  seated,  except  in  some  few  cases  where  this  is  im- 
possible ;  but  the  veins  are  often  superficially  situated.  You 
can  see  this,  for  example,  in  the  bend  of  the  arm.  Some  large 
veins  appear  there  just  under  the  skin,  while  the  artery  which 
supplies  the  arm  is  imbedded  among  the  muscles  and  tendons. 
In  every  part  of  the  body,  the  most  secure  spot  is  chosen  for 
an  artery.  Thus,  at  the  knee  joint,  the  artery,  instead  of  run- 
ning over  the  surface  of  bone,  where  it  would  be  liable  to  be 


68  HUMAN"  PHYSIOLOGY. 

Few  arteries  superficial.    Mode  of  stopping  the  bleeding  of  an  artery. 

wounded,  lies  deep  in  the  ham  at  the  rear  of  the  joint  The 
same  is  true  of  the  elbow  joint,  just  alluded  to,  and  of  other 
parts  of  the  body.  Although  there  are  arteries  everywhere, 
they  are  so  uniformly  deeply  seated,  that  it  is  only  in  a  few  lo- 
calities that  you  can  readily  find  one.  You  can  feel  one  pul- 
sating at  the  wrist,  and  also  on  the  temple.  Here  the  arteries 
are  superficial,  only  because  it  is  impossible  that  it  should  be 
otherwise. 

103.  When  the  physician  bleeds  a  patient,  he  commonly 
does  it  at  the  bend  of  the  arm,  as  being  the  most  convenient 
place  for  the  operation.     A  ligature  of  some  sort,  as  a  ribbon,  is 
tied  around  the  arm  above  the  elbow,  with  sufficient  tightness 
to  interrupt  the  flow  of  blood  toward  the  heart  in  the  super- 
ficial veins,  but  not  so  tightly  as  to  prevent  the  free  supply  of 
blood  to  the  arm  by  the  artery.     It  is  commonly  tied  as  tightly 
as  it  can  be  without  stopping  the  pulse  at  the  wrist.    An  open- 
ing is  then  made  in  one  of  the  veins ;  and,  as  the  blood  flows 
freely  into  the  arm  from  the  heart  through  the  artery,  on  its 
return,  so  much  of  it  as  passes  through  the  opened  vein  is  dis- 
charged at  that  point. 

104.  It  will  be  proper  here  to  give  some  practical  instruc- 
tion, in  regard  to  stopping  the  flow  of  blood  from  a  wounded 
arterv,  as  many  lives  have  been  lost  from  the  ignorance  of  by- 
standers when  such  accidents  have  happened.     Enveloping  the 
part  in  cloths,  which  is  so  commonly  done  at  such  times,  does 
no  good,  but  only  serves  to  catch  and  conceal  the  blood  as  it 
flows.     Pressure  upon  the  artery,  on  that  side  of  the  wound 
which  is  toward  the  heart,  will  of  course  interrupt  the  supply  of 
blood  from  this  organ  to  the  wound.     Firm  pressure  with  the 
thumb  will  do  it.     But  the  pressure  must  be  made  at  the  right 
point,  that  is,  directly  upon  the  artery.     You  may  not,  in  all 
cases,  press  upon  the  right  spot  at  once.     If  you  do  not,  the 
blood  will  continue  to  flow.     In  this  case,  press  at  different 
points,  until  you  find  the  point  at  which  you  see  that  pressure 
stops  the  flow  of  blood  from  the  wound.     But  you  may  not  be 
able  to  find  the  right  spot.      If  you  can  not,  you  can  *ie  a  slip 
of  strong  cloth  or  a  handkerchief  around  the  limb,  above  the 
wound,  and  twist  a  stick  in  it  until  the  bleeding  stops.     In  one 
or  the  other  of  these  ways,  you  can  prevent  the  loss  of  blood 
until  the  surgeon  arrives  to  take  charge  of  the  case. 

105.  Although  there  is  no  such  free  communication  between 
arteries  as  exists  between  the  capillaries,  there  is  some  amount 
of  communication,  and  particularly  in  certain  parts  of  the  body. 


THE   CIRCULATION.  69 

Aneurism.     Communication  between  arteries. 

And  it  is  well  that  it  is  so,  for  it  sometimes  helps  the  surgeon 
to  save  a  lirnb,  when  he  could  not  do  it  if  there  were  no  com- 
munication. I  have  already  alluded  to  a  disease  of  the  arteries 
called  aneurism.  An  artery  has  three  coats,  one  of  which  is  a 
strong  fibrous  one.  When  this  is  thinned  or  ruptured,  the 
other  two  coats  bulge  out,  forming  a  pulsating  tumour.  And, 
as  the  blood  is  constantly  pumped  into  this  by  the  force  of  the 
heart,  it  enlarges,  and  at  length  it  may  burst,  and  the  life  of 
the  patient  will  be  destroyed  by  the  loss  of  blood.  When  an 
aneurism  formed  in  a  limb,  as  for  example  in  the  ham,  the  sur- 
geon, in  former  times,  used  to  save  the  life  of  the  patient  by 
amputating  the  limb  above  the  aneurism.  Putting  a  ligature 
round  the  artery  above  the  aneurism  would  of  course  stop  the 
flow  of  blood  into  it ;  but  it  was  supposed  that  the  limb  would 
die,  in  that  case,  from  the  want  of  a  proper  supply  of  blood. 
But  it  was  found,  at  length,  that  this  was  not  so ;  and  surgeons 
now,  in  such  cases,  cure  the  disease,  and  save  the  limb  too,  by 
tying  the  artery.  Immediately  after  the  operation  the  limb  is 
cold,  and  there  is  plainly  very  little  circulation  in  it.  But  in  a 
few  hours  the  circulation  becomes  free,  and  in  a  little  time  it  is 
as  well  established  as  ever.  This  is  effected  by  the  communi- 
cations which  exist  between  the  branches  which  go  off  from  the 
artery  above  the  aneurism,  and  those  which  go  off  below  it. 
It  is  obvious,  however,  that  this  would  not  be  thoroughly 
effected  if  no  change  took  place  in  the  size  of  the  communicat- 
ing arteries.  But  this  change  does  occur.  Some  of  them  be- 
come enlarged  to  meet  the  necessity  of  the  case.  This  is  a 
most  interesting  fact ;  and  so  is  also  the  fact,  that  these  commu- 
nications between  branches  of  arteries  are  very  common  in  the 
neighborhood  of  those  places  in  the  body,  where  aneurism, 
from  strains  produced  by  violent  and  sudden  motion,  is  peculi- 
arly apt  to  appear.  This  same  provision  avails,  of  course,  when 
aneurism  is  cured  by  pressure  made  upon  the  artery  above  it, 
a  measure  which  modern  surgery  has  found  in  many  cases  to 
be  as  effectual  as  tying  the  artery. 

106.  There  have  been  great  differences  of  opinion  among 
physiologists,  in  regard  to  the  proportionate  amounts  of  agency 
that  the  different  parts  of  the  apparatus  have  in  carrying  on 
the  circulation.  The  heart  manifestly  exerts  the  chief  agency, 
both  by  its  forcing  and  its  suction  power.  You  can  get  a  clear 
idea  of  the  manner  in  which  it  exerts  these  two  forces  in  this 
way.  Fill  a  ball  of  India  rubber,  to  which  a  tube  is  attached, 
with  water,  and  immerse  the  tube  in  water  in  a  vessel.  If  you 


70  HUMAN  PHYSIOLOGY. 


Action  of  the  heart  illustrated.     Agency  of  the  capillaries  in  the  circulation. 

press  the  sides  of  the  ball  together,  some  of  the  water  is  forced 
out  into  the  vessel.  This  represents  the  contraction  of  the 
heart.  If,  now,  you  allow  the  ball  by  its  elasticity  to  resume 
its  round  shape,  the  water  rushes  into  it  from  the  vessel.  Tnis 
represents  the  dilatation  of  the  heart.  The  dilatation  of  the 
ball  results  from  its  elasticity ;  and  so  it  is  supposed  by  some 
that  the  dilatation  of  the  heart  results  from  the  same  cause,  its 
contraction  alone  being  produced  by  muscular  action.  Whether 
this  be  so  or  not,  the  dilatation  is  an  active  one,  and  the  blood 
rushes  into  the  heart  from  the  veins  by  suction,  as  it  is  termed. 
The  dilatation  is  so  active  that,  as  has  been  shown  by  experi- 
ments on  animals,  even  a  great  amount  of  pressure  is  not  able 
to  prevent  its  taking  place. 

107.  But,  great  as  the  agency  of  the  heart  is,  it  is  not  true 
that  it  is  the  only  moving  power,  and  that  the  arteries  and  veins 
are  mere  passive  conducting  tubes.   There  are  various  phenomena 
which  show  that  the  arteries,  the  capillaries,  and  even  the  lax 
veins,  exert  a  considerable  agency  in  circulating  the  blood.     I 
will  merely  allude  to  some   of  these  phenomena.     Determina- 
tions of  blood  to  particular  parts  show  that  the  blood-vessels 
have  an  active  agency  in  the  circulation.     In  inflammation  of 
any  part,  there  is  an  increased  activity  of  the  particular  portion 
of  the  circulating  apparatus  supplying  that  part.     In  the  act  of 
blushing,  there  is  a  local  activity  of  the  circulation  somewhat 
independent  of  the  heart.    This  is  also  true  of  the  circumscribed 
flush  of  hectic. 

108.  There  is  one  portion   of  the  circulation  in  which  the 
active  agency  of  the  capillaries  is  especially  manifest.      The 
veins,  as  I  have  told  you,  receiving  the  blood  from  all  parts  of 
the  body,  at  length  are  all  united  into  two  veins,  which  empty 
their  contents  into  the  heart.     But  there  is  a  very  remarkable 
exception  to  this.     The  veins  which  collect  the  blood  from  the 
viscera  in  the  abdomen  unite  in  one  large  trunk,  called  the  vena 
portae ;  and  this,  instead  of  pouring  its  contents  into  the  large 
vein  that  goes  up  to  the  heart,  divides,  like   an   artery,  into 
branches,  which  take  all  this  blood  to  the  liver  for  the  manufac- 
ture  of  bile.     Fig.  24  represents  this  circulation   of  the  vena 
porta3.    1,  1,  are  the  veins  coming  from  the  intestines  ;  2  is  the 
trunk  of  the  vena  portse  ;  and  3,  3,  are  the  branches  of  it  dis- 
tributed in  the  liver.     Now,  it  can  not  be  pretended  that  the 
suction  power  of  the  heart  extends  its  influence  through  the  veins 
that  bring  the  blood  from  the  liver,  then  through  the  capillaries 
of  this  organ,  and  then  through  all  the  veins  that  bring  the 


THE   CIRCULATION.  71 


Circulation  in  the  liver.    Why  the  veins  are  full  and  the  arteries  empty  after  death. 


1 
CIRCULATION  OF  VENOUS  BLOOD  IN  THE  LIVER. 

blood  to  the  liver,  even  to  the  capillaries  of  the  abdominal  vis- 
cera. There  must  be,  in  this  case,  some  propelling  power  in 
the  capillaries,  and  some,  too,  also  in  the  veins.  If  there  were 
not,  another  subordinate  heart  would  obviously  be  needed  in 
the  vena  portae,  to  pump  up  the  blood  from  all  the  veins  of  the 
abdominal  viscera,  and  then  to  send  it  through  all  its  branches 
into  the  capillaries  of  the  liver. 

109.  The  veins  have  a  less  active  agency  in  the  circulation 
than  any  of  the  other  parts  of  the  apparatus.  It  is  for  this 
reason  that  commonly  after  death  the  veins  are  found  quite 
full  of  blood,  while  the  arteries  are  nearly  empty.  The  appa- 
ratus of  the  circulation  may  be  regarded  as  forming  a  circle  of 
organs  in  this  order — the  heart,  the  arteries,  the  capillaries,  and 
the  veins.  The  blood  is  constantly  going  the  rounds  of  this 
circle.  It  is  plain  that,  as  the  apparatus  is  about  to  stop,  there 
must  be  an  accumulation  in  the  weakest,  least  active,  and  most 
relaxed  of  this  circle  of  organs.  The  arteries  and  capillaries  force 
the  blood  into  the  veins  to  the  last  moment  of  life.  This  effec* 


72  HUMAN   PHYSIOLOGY. 

The  blood  changed  in  the  capillaries  from  red  to  dark. 

probably  extends  no  further  than  the  smaller  veins ;  but  the  heart, 
by  its  active  dilatation,  draws  the  blood  from  them  into  the  larger 
veins.  And  as  these  two  forces,  at  the  two  ends  of  the  venous 
system,  are  at  work  up  to  the  last  moment,  the  whole  of  this 
system  is  filled  with  blood. 

110.  The  fact,  that  the  larger  arteries  are  commonly  found 
nearly  empty  of  blood  after  death,  gave  the  ancients  the  idea 
that  air  circulated  in  arteries,  while  blood  circulated  in  veins. 
Hence,  the  name,  artery,  is  derived  from  two  Greek  words,  sig- 
nifying to  hold  air.     And  hence,  also,  by  long  established  cus- 
tom, in  common  language,  the  blood  is  spoken  of  as  running  in 
our  veins;  and  it  would  sound  strangely,  if,  in  common,  and 
especially  in  poetical  language,  we  should  speak  of  it  as  running 
in  our  arteries  also.     Although  there  were  from  time  to  time 
some  glimpses  of  the  true  idea  of  the  circulation,  it  was  not 
really   developed   and  demonstrated   till    about   two  hundred 
and  thirty  years  ago.     Harvey  spent  eight  years  in  maturing 
his  ideas  on  the  subject.     When  he  published  them,  they  en- 
countered much  opposition ;  but  he  lived  long  enough  to  see 
them  almost  universally  received  by  the  medical  world,  although 
the  profession  was  in  a  much  less  enlightened  state  than  it  is  at 
the  present  day. 

111.  I  will  now  take  you  a  step  farther  in  the  development 
of  the  plan  of  the  circulation.     I  have  said  that  the  office  of 
the  arteries  is  to  conduct  the  blood  to  the  network  of  capil- 
laries, and  that  in  the  capillaries  the  blood  has  reached  its 
place  of  destination  where  it  is  to  be  used.     The  formative  ves- 
sels, appended  to  the  capillaries,  take  from  the  blood  what  they 
need  for  their  various  purposes,  and  at  the  same  time  there  is 
added  to  the  blood  refuse  matter  from  the  waste  of  the  tissues. 
The  blood,  then,  is  changed  while  it  is  in  the  capillaries.     You 
see  the  change  in  its  color.     In  the  arteries  it  was  red ;  but, 
after  passing  through  the  capillaries,  it  appears  in  the  veins  of 
a  purple  color.     It  is  also  as  much  changed  in  other  properties. 
It  is  no  longer  fitted  to  nourish  the  body.     It  would  even  prove 
a  poison  to  any  organ  if  it  should  flow  into  its  capillaries.     If  it 
should,  for  example,  be  sent  to  the  brain,  instead  of  bright  ar- 
terial blood,  that  organ  would  cease  to  do  its  office  ;  insensibility 
would  ensue,  and  life  would  soon  be  destroyed,  if  the  flow  of 
red  blood  could  not  be  established. 

112.  This  purple  blood,  which  comes  back  to  the  heart  from 
the  capillaries  by  the  veins,  must,  therefore,  be  in  some  way 
changed  to  red  blood,  before  it  is  again  sent  all  over  the  system 


THE  CIRCULATION.  73 


Change  in  the  blood  in  the  lungs.     Course  of  the  circulation 

through  the  arteries.  This  change  is  effected  in  the  lungs.  As 
the  purple  blood  returns  to  the  heart,  it  is  sent  by  the  heart  to 
the  lungs,  in  order  to  be  exposed  to  the  air  before  it  is  sent 
again  over  the  system.  For  this  purpose  there  are  two  circula- 
tions, and  the  heart  is  a  double  organ ;  or  rather,  there  are  in 
effect  two  hearts  for  the  two  circulations,  for  the  two  sides  of 
the  heart  have  no  communication  with  each  other.  The  appa- 
ratus for  all  this  is  very  complicated,  but  I  think  it  can  be  made 
clear  to  you. 

113.  I  present,  first,  a  diagram,  which  is  intended  to  repre- 
sent merely  the  course  of  the  circulation,  without  regard  to 
proportionate  size,  or  to  minutiae  in  the  arrangement  of  the  ap- 
paratus. Let  a  represent  the  right  side  of  the  heart,  c  the  left 
side,  b  the  lungs,  and  d  the  general  system  of  the  body.  The 
arrows  show  the  direction  in  which  the  blood  flows.  In  all  the 
shaded  part  the  blood  is  venous  or  purple,  and  in  the  part  not 
shaded  it  is  arterial  or  red.  We  will  now  take  some  point  of 
beginning,  and  trace  on  the  Figure  the  course  of  the  circulation. 

PIG.  25. 


DIAGRAM  SHOWING  THE  COURSE  OF  THE  CIRCULATION". 

We  will  start  at  a,  the  right  side  of  the  heart.  The  blood  re- 
ceived here,  of  a  purple  color,  from  the  whole  body  by  the 
veins,  is  sent  by  the  heart  to  ft,  the  lungs.  Here  it  changes  to 
red  blood,  and  passes  by  veins  back  to  the  heart — but,  observe, 
it  is  to  the  left  side  of  the  heart,  c.  It  is  now  sent  by  this  left 
half  of  the  heart  to  all  parts  of  the  system,  represented  by  d. 
Here,  in  the  capillaries,  it  is  changed  to  purple  blood,  and  goes 
back  by  veins  to  the  right  side  of  the  heart,  a,  the  place  where 
we  started. 

7 


74  HUMAN   PHYSIOLOGY. 


Two  circulations  and  two  hearts.     Arrangement  of  valves. 

114.  You  see,  then,  that  there  are  two  separate  circulations, 
one  through  the  general  system,  and  the  other  through  the  lungs 
alone.     In  both  circulations  the  blood  is  sent  from  the  heart 
by  arteries,  and  is  brought  back  to  it  by  veins.    But  notice  that, 
while  in  the  general  circulation  the  red  blood  is  in  the  arteries, 
and  the  purple  in  the  veins,  in  the  circulation  through  the  lungs 
it  is  reversed — the  red  blood  is  in  the  veins,  and  the  purple  is 
in  the  arteries.     So,  also,  while  the  change  of  the  blood  in  the 
capillaries  of  the  general  system  is  from  red  to  purple,  in  the 
capillaries  of  the  lungs  it  is  from  purple  to  red. 

115.  There  are  not  only  two  sides  or  halves  of  the  heart, 
separated  entirely  from  each  other,  but  each  of  these  sides  has 
two  apartments,  with  valves  or  folding  doors  between  them,  so 
arranged  that  the  blood  can  pass  one  way  through  them,  but 
not  the  other.     There  are  also  valves  at  the  beginning  of  the 
great  artery  of  the  heart,  the  aorta.     These  are  so  arranged 
that  the  blood  can  go  freely  out  of  the  heart  into  the  artery, 
but  not  a  drop  can  get  back  from  the  artery  into  the  heart. 
There  are  similar  valves,  also,  at  the  beginning  of  the  great  ar- 
tery, by  which  the  purple  blood  is  sent  from  the  heart  to  the 
lungs. 

116.  In  Fig.  26,  is  represented  a  section  of  the  right  side  of 
the  heart,  for  the  purpose  of  giving  you  an  idea  of  the  arrange- 
ment and  the  relative  size  of  the  two  apartments.     The  auricle, 
a,  so  called   because  a  part  of  it  has   some  resemblance  to 
an    ear,  receives  the  blood  from   the  whole  system  by  two 
large  veins,  6,  b,  called  the  venae  cavte. 

From  the  auricle  it  passes  into  the  ven-  FIG.  26. 

tricle,  v,  which  by  its  contractions  sends  a 

it  to  the  lungs  through  the  pulmonary 
artery,  /.  The  valve  between  the  au- 
ricle and  ventricle  is  composed  of  three 
membraneous  sheets,  which  are  held  at 
their  edges  by  small  tendinous  cords,  o?, 
just  as  a  sail  is  held  by  the  ropes  at  its 
corners.  This  valve  permits  the  blood 
to  pass  from  the  auricle  into  the  ventri- 
cle ;  but  when  it  attempts  to  pass  back 
from  the  ventricle  to  the  auricle,  it  SECTION  OF  THE  RIGHT 
pushes  back  the  sheets  of  the  valve,  they  SIDE  OF  THE  HEART. 
being  prevented  from  going  too  far  back 

by  the  tendinous  cords.    There  are  also  valves  at  e,  the  beginning 
of  the  pulmonary  artery,  which  allow  the  blood  to  pass  through 


THE  CIRCULATION.  75 


Relation  between  the  auricles  and  the  ventricles. 


them  into  the  artery,  but  no  blood  can  pass  through  them  from 
the  artery  back  into  the  ventricle.  I  shall  soon  call  your  atten- 
tion again  to  these  different  valves,  that  you  may  see  more  par- 
ticularly their  structure  and  arrangement. 

117.  The  auricle  and  ventricle  act  in  this  way  in  propelling 
the  blood.     When  the  auricle  contracts,  the  ventricle  dilates  * 
to  receive  the  blood  from  the  auricle.    The  valves  between  them 
are  open  while  this  is  taking  place.     But  the  next  moment  the 
ventricle  contracts  and  the  auricle  dilates.     You  at  once  see, 
that  if  now  the  valves  between  them  should  be  open,  the  blood 
would  be  forced  back  into  the  auricle.     But  the  membranous 
sheets  of  these  valves  shut  upon  each  other  as  the  ventricle 
contracts,  and  thus  prevent  the  blood  from  going  back.     It 
therefore  is  discharged  through  the  pulmonary  artery,  /,  the 
valves  there  being  open.     And  when  the  ventricle  dilates,  you 
can  see  that  the  blood  would,  from  suction,  enter  it  from  the 
artery  as  well  as  from  the  auricle,  if  the  valves  at  the  orifice  of 
the  artery  should  remain  open.     They  are   accordingly  shut 
when  the   ventricle  dilates.      You   see,   then,  that  when  the 
auricle  dilates  and  the  ventricle  contracts,  the  valves  between 
the  auricle  and  ventricle  are  closed,  and  the  valves  at  the  mouth 
of  the  pulmonary  artery  are  open ;  and,  on  the  other  hand, 
when  the  ventricle,  dilates  and  the  auricle  contracts,  the  valves 
between  them  are  open,  and  the  valves  of  the  pulmonary  artery 
are  closed. 

118.  Dr.  Carpenter  has  a  very  good  illustration  of  the  rela- 
tion of  the  actions  of  the  auricle  and  ventricle,  in  a  representa- 
tion given  in  Fig.  27.     The  apparatus  which  is  represented 
consists  of  two  pumps,  a  and  6,  the  pistons  of  which  move  up 
and  down  alternately.     These  are  connected  with  a  pipe,  c,  /, 
in  which  there  are  two  valves,  d  and  e,  opening  in  the  direction 
of  the  arrows.     The  portion  c  of  the  pipe  represents  the  venous 
trunk  discharging  its  blood  into  the  heart,  and  the  portion  /, 
the  artery  which  is  the  outlet  for  the  blood.     The  pump,  a, 
represents  the  auricle,  and  the  pump,  6,  the  ventricle.     When 
the  piston  in  a  is  raised,  the  fluid  enters  through  c  to  fill  it  by 
suction,  as  it  is  termed.     When,  now,  its  piston  is  lowered,  the 
fluid  is  forced  through  the  valve  d  into  the  pump  6,  (which  re- 
presents the  ventricle,)  whose  piston  is  at  the  same  time  raised 
to  receive  it.     And  when  the  piston  in  b  is  lowered  in  its  turn, 


*  This  dilatation  is  an  active  one,  as  was  stated  in  §  106,  when  speaking  of  the  heart 
as  a  whole.  The  ventricle  does  not  dilate  because  the  blood  is  forced  into  it,  but  the 
blood  rushes  into  it  because  it  dilates. 


76 


HUMAN   PHYSIOLOGY 


Ventricles  larger  and  stronger  than  the  auricles.     Valves  of  the  aorta. 


FIG.  27. 


a 


db 


the  fluid  being  prevented  from  returning  into  a,  by  the  closure 
of  the  valve  d,  is  forced  through  the  valve  e  into  /,  representing 
the  discharging  tube,  the  artery.  At  the  same  time,  a  fresh 
supply  of  fluid  is  received  into  a  by  the  raising  of  its  piston. 

119.  I  have  described  the  auricle  and  ventricle  of  one  side 
of  the  heart,  the  right  side.      The  left  side  is  constructed  very 
much  in  the  same  way.     You  will  observe,  in  Fig.  26,  that  the 
ventricle  is  much  more  capacious  than  the  auricle.     The  auricle 
is  indeed  the  antechamber  to  the  ventricle.      The   ventricle, 
too,  you  see,  is  much  thicker  in  its  walls.     It  is  made  very 
strong,  because  it  does  by  far  the  principal  part  of  the  work. 
I  remark  here,  in  passing,  that  the  size  of  the  whole  heart  is 
about  that  of  the  closed  hand  of  the  individual. 

120.  I  will  now  call  your  attention  to  a  more  particular  view 
of  the  valves  of  the  heart.     We  will  take,  first,  the  valves 
which  are  at  the  beginning  of  the  aorta,  the  great  artery  of  the 
body,  going  out  from  the  left  ventricle.     These  are  very  much 
like  the  valves  of  the  veins  seen  in  Fig.  23.     There  are  three 
of  them.     They  are  like  little  pockets  arranged  around  the  ori- 
fice of  the  artery,  and  looking  toward  the  tube  of  the  artery. 
Of  course,  when  the  ventricle  contracts,  and  forces  the  blood 
into  the  artery,  these  pockets  are  pressed  by  the  blood  flat 
against  the  sides  of  the  artery.     But  when  the  ventricle  dilates, 
and  the  blood  attempts  to  go  back  from  the  artery  into  the 
ventricle,  it  gets  into  these  pockets,  and  bulges  them  out  toward 
the  heart,  and  thus  the  mouth  of  the  artery  is  closed.    But  you 
can  see  that  if  these  pocket-like  valves  had  plain  curved  edges, 
they  would  not  effect  a  perfect  closure.     There  would  be  a 


THE   CIRCULATION. 


77 


Peculiar  provision  in  the  valves  of  the  aorta. 


FIG.  28. 


little  space  in  the  very  middle  of  the  orifice  of  the  artery  which 
would  be  left  open.  This  is  made  plain  by  Fig.  28,  which  pre- 
sents the  orifice  of  the  artery  with 
its  closed  valves,  as  it  would  appear 
seen  from  the  interior  of  the  heart, 
if  the  three  valves  had  plain  curved 
edges.  There  would  be  a  space  left 
between  them.  But  this  difficulty  is 
remedied  by  a  very  simple  contriv- 
ance. A  little  fleshy  projection  is 
placed  upon  the  middle  point  of  the 
edge  of  each  valve,  of  such  a  size 
that  the  three  projections  together 
just  fill  the  space  A.  When,  there- 
fore, the  valves  are  closed,  no  blood 
can  go  back  from  the  artery  into  the 

ventricle.  This  arrangement  is  shown  in  Fig.  29,  in  which  the 
aorta,  a,  is  laid  open  and  spread  out,  so  as  to  show  the  three 
valves  with  their  projections  on  the  edges.  At  6  and  c,  are  the 
openings  of  the  two  arteries  that  supply  the  walls  of  the  heart 


FIG.  29. 


VALVES  OF  THE  AORTA. 


with  blood  for  their  growth  and  repair,  tor  the  heart  is  con- 
structed and  repaired  from  its  own  blood.  The  valves  at  the 
orifice  of  the  pulmonary  artery  are  arranged  in  the  same  man- 
ner as  those  which  are  at  the  orifice  of  the  aorta. 

121.  The  valves  which  are  between  the  auricles  and  the 
7* 


78  HUMAN  PHYSIOLOGY. 


Arrangement  of  the  valves  between  the  auricles  and  ventricles. 

ventricles  I  have  already  partially  described.  They  are  folds 
of  strong  white  membrane,  their  edges  being  held  by  numerous 
small  tendinous  cords.  And  these  cords  are  manned,  as  we  may 
express  it,  by  muscles  attached  to  the  walls  of  the  heart.  The 
office  of  these  muscles  is  to  hold  on  to  the  cords  that  are  fast- 
ened to  the  edges  of  the  valves,  and  prevent  these  sheets  of 
membrane  from  flapping  back  too  far  when  the  powerful  ven- 
tricle contracts.  It  is  by  a  nice  adjustment  of  forces  that  these 
valves  act  with  such  exactness.  They  are  of  greater  extent 
than  the  valves  which  are  at  the  mouth  of  the  aorta  and  the 
pulmonary  artery,  and,  therefore,  it  would  not  do  to  leave  them 
to  act  alone,  as  those  valves  do,  upon  simple  mechanical  princi- 
ples. The  living  muscular  fibre  must  be  introduced  as  the 
agent  to  control  and  regulate  these  principles  in  their  applica- 
tion here.  If  it  were  not  done,  the  consequence  would  be,  that 
when  the  ventricle  contracts  with  prodigious  force,  as  it  some- 
times does  when  the  circulation  is  in  a  great  state  of  excitement, 
the  light  tendinous  fastenings  would  be  ruptured  by  the  pres- 
sure of  the  blood  upon  the  valves.  As  it  is  now,  the  strong 
but  yielding  muscular  bundles,  to  which  these  tendons  are 
attached,  regulate  with  great  exactness  the  closing  of  the  valves. 
Even  if  there  were  no  need  of  any  regulation,  by  muscular 
action,  of  the  movement  of  these  valves — if  the  tendons  would, 
in  all  cases,  let  the  valves  go  back  to  just  the  right  point — as 
they  are  not  extensible,  and  have  no  elasticity,  it  is  manifest 
that  there  would  be  more  danger  of  rupture  than  there  is  with 
the  present  arrangement.  The  tendons  cannot  be  stretched,  and, 
therefore,  under  great  pressure  they  might  break.  In  Fig.  30 
is  a  representation  of  a  portion  of  this  valvular  apparatus.  The 
engraving  was  made  from  a  drawing  of  the  part  taken  from 
the  heart,  and  pinned  upon  a  board  for  the  purpose.  At  m, 
you  see  the  sheet  of  membrane ;  o,  o,  are  two  of  the  muscles 
attached  to  the  inside  of  the  ventricle,  to  hold  on  to  the  ten- 
dons, A,  that  are  fastened  to  the  edge  of  the  membrane.  This 
membrane  is  now  in  the  position  that  it  is  when  the  valves  are 
open,  that  is,  lying  in  a  line  with  the  little  tendons  and  their 
muscles.  But  when  the  ventricle  contracts,  the  blood,  pushing 
against  the  membrane  m,  carries  up  the  free  edge  to  which  the 
tendons  are  fastened,  which,  meeting  the  free  edges  of  the  other 
valves,  closes  with  them  the  communication  between  the  auricle 
and  ventricle. 

122.  In  looking  at  Fig.  26,  you  observe  that,  while  there  are 
valves  between  the  auricle  and  ventricle,  and  at  the  mouth  of 


THE   CIRCULATION.  79 


No  valves  at  the  openings  of  the  venae  cavse.    Why  this. 


FIG.  30. 


PART  OF  THE  VALVULAR  APPARATUS  BETWEEN  THE  AURICLE 
AND  THE  VENTRICLE. 

the  artery  going  out  from  the  ventricle,  there  are  none  at  the 
openings  of  the  two  ven<#  cava,  the  veins  that  pour  their  con- 
tents into  the  auricle.  Why  is  this  ?  Why  is  there  no  need 
of  valves  here  to  prevent  a  regurgitation  into  these  veins  when 
the  auricle  contracts  ?  It  is  because  that,  as  the  auricle  con- 
tracts, there  is  at  the  same  time  the  dilatation  of  the  strong 
ventricle,  making,  of  course,  a  suction  in  that  direction  so 
powerful  as  to  counteract  most  fully  any  tendency  to  regurgita- 
tion into  the  veins.  You  readily  see,  that  if  the  arrangement 
were  reversed,  and  the  auricle  were  stronger  than  the  ventricle, 
then,  when  the  auricle  contracted,  there  would  be  regurgitatior 
into  the  vena?  cavge,  if  there  were  no  valves  there  to  prevent  it. 
The  same  remarks  could  be  made  in  regard  to  the  pulmonary 
veins,  that  pour  their  contents  into  the  left  auricle. 

123.  Having  thus  examined  the  heart  in  detail,  you  are  now 
prepared  to  look  at  it  as  a  whole.  For  this  purpose,  I  present 
to  you,  in  Fig.  31,  a  front  view  of  the  heart,  in  which  a  is  the 
right  auricle,  receiving  the  purple  blood  from  the  whole  body 
by  the  two  large  veins,  h  and  i,  called  the  ve nee  cav<z  j  b  is  the 
right  ventricle,  that  receives  the  blood  from  the  right  auricle, 
and  sends  it  to  the  lungs  by  the  pulmonary  artery,  f  ;  c  is  the 
left  auricle,  which  receives  the  red  blood  from  the  lungs,  by 
the  pulmonary  veins,  g,  g,  a;  d  is  the  left  ventricle  that  re- 
ceives the  blood  from  the  left  auricle,  and  sends  it  all  over  the 
body  through  the  aorta,  e.  You  observe,  that  you  see  but  a 
part  of  the  left  auricle  and  ventricle,  they  lying  partly  behind 
Mie  right  ventricle.  You  do  not  see  the  very  beginning  of  the 


80 


HUMAN   PHYSIOLOGY. 


General  view  of  all  the  parts  of  the  heart. 


FIG.  31. 


FRONT  VIEW  OF  THE  HEART. 


aorta,  for,  as  it  rises  from  the  left  ventricle  it  is  at  first  con- 
cealed behind  the  top  of  the  right  ventricle  and  the  beginning 
of  the  pulmonary  artery.  It  then  forms  an  arch,  from  which 
it  sends  forth  branches  to  the  head  and  upper  extremities ;  and 
it  afterwards  passes  down  behind  the  heart,  to  supply  with  its 
branches  the  trunk  of  the  body  and  the  lower  extremities.  In 
the  line  of  division  between  the  two  ventricles,  b  and  d,  you 
see  one  of  the  coronary  arteries,  as  they  are  called,  which, 
coming  from  the  beginning  of  the  aorta,  as  describedjn  §  120, 
supply  the  walls  of  the  heart  with  blood.  '4|p 

124.  To  make  you  quite  familiar  with  the  relations  of  the 
different  parts  of  this  complicated  organ,  and  with  the  course 
of  the  blood  through  its  different  apartments,  I  give  vou,  in 


THE   CIRCULATION. 


81 


Course  of  the  blood  through  the  different  cavities  of  the  heart. 

Fig.  32,  a  map  of  the  heart,  with  the  names  pHiced  upon  the 
parts.  I  will  describe  the  circulation  with  this  map  before  you. 
The  dark  blood  is  received  from  all  parts  of  the  body  by  the 
venae  cav<e — from  the  parts  above  by  the  descending  cava,  and 


FIG.  32. 


MAP  OF  THE  CIRCULATION. 


from  the  parts  below  by  the  ascending  cava.  These  veins  pour 
the  blood  into  the  right  auricle.  From  this  it  passes  into  the 
right  ventricle,  wl^h  sends  it  by  the  pulmonary  artery  to  the 
lungs.  Fr^tffflfllmgs  it  returns  by  the  pulmonary  veins  to 
the  left «  B^^  ^nen  Passes  mt°  tne  left  ventricle,  from 
which  itiBMBby  the  aorta  to  all  parts  of  the  body. 

125.  In  Fig.  33  is  represented  the  heart,  situated  between 
the  two  lungs,  with  the  arteries  which  carry  blood  from  it,  and 


82 


HUMAN  PHYSIOLOGY. 


Situation  and  connections  of  the  heart.     Its  harmonious  action. 

the  veins  whic^i  pour  their  blood  into  it.  The  lungs  are  repre- 
sented as  being  drawn  apart  to  the  right  and  left  in  front,  so 
as  to  expose  fully  the  heart  and  its  vessels.  The  sac  containing 
the  heart,  and  the  packing  cellular  tissue  are  removed,  so  as  to 
lay  the  heart  and  its  vessels  bare.  At  a  is  the  trachea  or  wind- 
pipe ;  on  either  side  of  it  are  the  two  arteries,  the  carotids, 
which  go  to  the  head ;  c  is  the  artery  which  goes  to  the  arm ; 
6,  6,  are  the  jugular  veins  coming  from  the  head,  d,  c?,  the  veins 


e         f  g  h          i 

LUNGS,  HEART,  AND  PRINCIPAL  BLOOD-VESSELS. 


from  the  arms,  all  empting  their  contents,  as  you  see,  into  the 
descending  cava;  e  is  the  right  auricle,  receiving  the  blood 
from  the  two  cavae ;  /  the  ascending  cava ;  g  the  right  ventri- 
cle, i  the  left  ventricle,  and  h  the  descending  aorta. 

126.  I  have  been  thus  particular,  and  have  led  you  through 
some  repetitions  in  the  description  of  some  of  the,  figures,  in 
order  that  you  may  get  a  clear  idea  of  the  c^jft^Hcated  mecha- 
nism of  the  circulation.  And  now,  perhaps^BJ  iiunqiiire, 
in  what  way  all  these  four  apartments  of  thew((Hfrcontract 
and  dilate,  so  as  to  have  the  organ  act  as  one  harmonious 
whole.  You  have  seen  how  the  auricle  and  ventricle  of  one 


THE   CIRCULATION.  83 


The  causes  of  the  two  sounds  of  the  heart.    Its  forward  impulse. 

side  act  in  relation  to  each  other — the  auricle  contracts  when 
the  ventricle  dilates,  and  the  ventricle  contracts  when  the  auri- 
cle dilates.  Now,  the  harmony  of  action  between  the  two  sides 
is  preserved  by  having  the  two  auricles  act  together,  and 
the  two  ventricles  act  together.  And  this  action  produces 
two  sounds,  which  may  be  heard  by  applying  the  ear  to  the 
chest  of  any  one  on  the  left  side.  The  first  sound  is  rather 
a  prolonged  and  heavy  one,  the  second  is  light  and  quick. 
They  are  very  well  represented  by  the  syllables  lub-tup.  The 
first  sound  occurs  when  the  strong  action  of  the  heart  is  per- 
formed, that  is,  when  the  ventricles  contract.  It  is  owing 
to  several  causes.  One  of  these  is  the  impulse  of  the  heart 
against  the  walls  of  the  chest;  the  cause  of  which  I  shall 
speak  of  soon.  Another  is  the  flapping  together  of  the 
valves  between  the  auricles  and  the  ventricles,  to  prevent  the 
blood  from  regurgitating  into  the  auricles,  when  the  ventricles 
contract  to  force  out  their  contents.  The  light  and  quick 
second  sound  is  caused  principally  by  the  flapping  together  of 
the  valves  at  the  mouths  of  the  aorta  and  the  pulmonary 
artery  when  the  ventricles  dilate.  The  pulse  (which  I  have 
already  remarked  upon  in  §  100)  is  produced  by  the  impulse 
given  to  the  blood  by  the  contraction  of  the  ventricles.  There 
is,  therefore,  a  pulse  in  the  arteries  of  the  circulation  through 
the  lungs,  as  well  as  in  those  of  the  circulation  through  the 
general  system.  Wherever  there  is  an  artery  there  is  pulsation. 
127.  The  impulse  of  the  heart  against  the  front  wall  of  the 
chest  on  the  left  side  is  easily  explained.  The  heart  is  so  en- 
veloped by  the  lungs,  that  only  a  small  portion  of  it  comes 
near  to  the  front  wall  of  the  chest,  and  such  is  the  situation  of 
the  heart,  that  this  portion  comes  to  the  left  of  the  middle  line 
of  the  chest.  The  position  of  the  heart  is  an  oblique  one,  its 
upper  part  being  both  farther  back  and  more  to  the  right  than 
its  lower  part.  Keeping  in  view  this  position  of  the  heart,  you 
will  readily  see  how  the  impulse  is  produced  against  the  front 
of  the  chest  at  its  lower  part.  The  aorta,  in  going  from  the 
heart,  makes  an  arch  upward  and  backward,  to  go  down  in 
front  of  the  spire ;  and  it  is  the  tendency  to  straighten  out, 
produced  in  this  arch  by  the  force  of  the  blood  thrown  into  it 
by  the  ventricle,  that  causes  the  throwing  of  the  heart  forward 
by  a  spring.  This  is  easily  seen  as  illustrated  by  Fig.  34,  in 
which  a  is  the  spinal  column  ;  6,  the  front  wall  of  the  chest ; 
d,  the  heart ;  and  c,  the  arch  of  the  aorta.  When  the  heart 
throws  the  blood  inio  this  arched  tube  it  tends  to  straighten  it; 


84 


HUMAN  PHYSIOLOGY. 


Arrangement  of  the  sac  of  the  heart.    Its  lubrication. 


but,  as  the  aorta  is  fastened  to  the 
fixed  spine  behind,  there  can  be  no 
impression  made  in  that  direction.  FIG- 34- 

The  straightening  of  the  arch  must 
therefore  occur  in  the  other  direction, 
to  the  front ;  and  therefore  the  heart 
is  thrown  a  little  forward,  as  represent- 
ed by  the  dotted  lines.  The  change 
of  position  thus  produced  is  indeed 
but  slight,  but  it  is  sufficient  to  cause 
the  impulse.  The  entrance  of  the 
blood  into  the  pulmonary  artery  per- 
haps aids  in  the  result,  but  not  very 
materially. 

128.  The  heart,  as  I  have  already 
hinted,  is  inclosed  in  a  sac,  called  the 
pericardium,  which,  at  its  upper  part, 

is  fastened  all  around  the  vessels  that  proceed  from  the  heart. 
This  sac  is  lined  on  the  inside  by  a  serous  membrane,  which  also 
lines  the  outside  of  the  heart,  being  reflected  over  upon  it  from 
the  pericardium.  This  membrane  forms,  therefore,  a  sac  without 
any  outlet.  This  is  made  plain  by  Fig.  35.  In  this  diagram, 
showing  the  plan  of  the  serous  membrane  of  the  pericardium, 
a,  a  are  the  auricles ;  v,  v,  the  ventricles ;  6,  c,  the  vessels  pro- 
ceeding from  the  heart ;  p  the  serous  membrane  lining  the  out- 
side of  the  heart ;  j/,  the  same  membrane  reflected  from  the 


FIG.  35. 


V....- 

PLAN  OF  THE  PERICARDIUM. 


CIKCULATTOtf.  85 


Action  of  the  heart  involuntary.     Number  of  its  beats. 


upper  part  of  the  heart  on  to  the  inside  of  the  pericardium. 
The  arrangement  of  this  membrane,  as  it  fits  on  to  the  heart, 
is  much  like  the  common  double  nightcap,  as  it  fits  on  to 
the  head ;  and  if  it  were  dissected  off  whole  from  the  outside 
of  the  heart  and  the  inside  of  the  pericardium,  it  would  be 
like  such  a  nightcap  when  taken  off  from  the  head — that  is,  a 
sac  without  an  outlet.  Now,  this  sac  is  kept  moistened  by  a 
fluid  exuding  from  its  whole  surface,  so  that,  as  that  part  of  it 
which  lines  the  outside  of  the  heart,  in  the  motions  of  that 
organ,  rubs  against  that  part  which  lines  the  pericardium,  the 
lubrication  prevents  any  injury  from  the  friction.  This  lubri- 
cating fluid  is  continually  renewed,  the  exhalents  and  the  absorb- 
ents balancing  each  other  in  their  action.  When  the  exhalents 
secrete  more  fluid  than  the  absorbents  can  take  up,  it  accumu- 
lates, making  what  is  cafled  dropsy  of  the  heart. 

129.  The  heart,  as  you  have  seen,  is  a  complex  arrangement 
of  muscles.  And  these  muscles  are  wholly  involuntary ;  that 
is,  they  are  not  at  all  under  the  direct  control  of  the  will.  No 
one  can  by  an  exercise  of  the  will  make  his  heart  beat  slower 
or  faster.  As  I  shall  show  you  in  another  chapter,  this  organ 
is  kept  at  work  by  its  nervous  connection  with  the  spinal  mar- 
row. It  has  no  repose,  as  the  voluntary  muscles  have,  unless 
you  call  the  intervals  between  the  contractions  and  dilatations 
of  its  several  parts  intervals  of  repose.  The  amount  of  work 
which  it  does  is  enormous,  if  we  calculate  it  for  a  lifetime. 
The  heart  of  an  adult  beats,  that  is,  each  one  of  the  four  cham- 
bers of  this  organ  dilates  and  contracts,  about  70  times  in 
a  minute.  This  would  make  100,800  times  in  24  hours, 
36,792,000  times  in  a  year,  and  2,575,440,000  times  in  a  life 
of  70  years.  In  children,  the  action  of  the  heart  is  much  more 
rapid,  and  in  disease  it  sometimes  reaches  in  them  to  160  or 
even  200  beats  in  a  minute.  It  is  thus  that  this  organ,  situ- 
ated in  the  centre  of  the  complicated  apparatus  of  the  circula- 
tion, labors  continually,  by  night  and  by  day,  in  keeping  the 
blood  in  motion.  The  two  circulations  of  the  general  system 
and  of  the  lungs  are  ever  going  on.  The  blood  is  ever  moving 
in  all  the  cavities  of  the  heart,  in  every  artery,  and  vein,  and 
capillary.  It  never  stops  till  it  is  arrested  by  death. 


86  HUMAN   PHYSIOLOGY. 

Apparatus  of  respiration.     Air-ceils  in  the  lungs.    Their  size. 


CHAPTER  VII. 

RESPIRATION. 

130.  You  saw,  in  the  last  chapter,  that  the  purple  venous 
blood  is  sent  to  the  lungs  to  be  changed  into  arterial  blood. 
The  great  object  of  the  apparatus  of  respiration  is  to  introduce 
the  air  to  the  blood,  so  that  it  may  act  upon  it,  and  produce 
this  change.     Another  object  is  effected  at  the  same  time,  viz., 
the  production  of  the  voice,  by  the  striking  of  the  air  upon 
the  vocal  chords  in  the  larynx,  as  it  is  forced  out  from  the 
lungs.     This  will  be  made  the  subject  of  a  future  chapter,  and 
I  propose  now  to  show  how  the  chief  object  of  respiration, 
which  is  so  immediately  essential  to  the  continuance  of  life,  is 
secured. 

131.  The  lungs  are  spongy  bodies,  filling  up  a  large  part  of 
the  chest,  and  surrounding  the  heart.     They  are  in  common 
language,  the  lights ;  and  you  can  see  what  they  are  in  man 
by  observing  the  lights  of  other  animals.     They  are  composed 
chiefly  of  air-tubes,  air-cells,  blood-vessels,  and  nerves,  packed 
together  with  the  common  packing  material  of  the  body,  cellu- 
lar membrane.     The  spongy  lightness  of  the  lungs  is  owing  to 
the  air-cells  or  vesicles.     You  can  get  some  idea  of  the  propor- 
tion of  these  cells   to  the  solid  part  of  the    organs  if  you 
inflate  the  lungs  of  some  animal,  as  the  sheep  or  calf,  by  blow- 
ing into  the  windpipe.     These  cells  are  exceedingly  minute. 
It  is  in  them  that  the  change  is  effected  in  the  blood.     The 
capillaries  holding  the  blood  branch  out  on  the  walls  of  the 
cells,  and  the  blood  is  acted  upon  by  the  air  through  the  pores 
of  the  vessels.     The  object,  therefore,  of  respiration  is  to  in- 
troduce the  air  freely  into  these  cells.      The  air  enters  through 
the  windpipe,  and  this  branches  out  into  tubes  called  bronchi, 
which  divide  and  subdivide,  till  they  become  very  minute,  and 
then  end  in  the  air-cells.    These  cells  are  estimated  to  be  about 
the  To~oth  of  an  inch  in  diameter.      Some  calculations  have 
been  made  in  regard  to  the  extent  of  surface  which  they  would 
all  make  if  they  could  be  spread  out  in  one  sheet.    There  is  of 
course  no  great  accuracy  in  such  calculations ;  but  we  can  readily 
see  that  the  aggregate  surface  must  be  immense,  and,  therefore, 
the  blood  is  thus  very  extensively  exposed  to  the  action  of  the 


RESPIRATION.  87 


Air-tubes.     Relative  situation  of  the  lungs  and  the  heart. 

air.  In  Fig.  36  is  represented  the  lung  of  one  side,  d ;  the 
branches  of  the  bronchi  of  the  other  lung,  c,  at  the  lower  part 
of  which,  <?,  they  are  represented  as  they  branch  put  minutely 
to  open  into  the  air-cells ;  b  is  the  trachea  or  windpipe,  and  a 


LUNGS  AND  AIR-TUBES. 


is  the  larynx  at  the  top  of  it.  It  is  through  a  chink  called  the 
glottis,  in  the  larynx,  that  all  the  air  passes  as  it  goes  into  and 
out  from  the  lungs.  This  will  be  particularly  described  here- 
after. 

132.  In  Fig.  33,  in  the  last  chapter,  you  see  represented  the 
relative  situation  of  the  heart  and  lungs,  the  lungs  being  some- 
what separated,  however,  from  the  heart,  to  the  right  and  left, 
in  order  to  show  that  organ  fully.  In  their  natural  position 
they  are  close  to  the  heart,  and  cover  up  all  of  it,  except  a 
small  portion  in  front  and  to  the  left  side,  where  its  beating  is 
so  plainly  felt.  Both  the  heart  and  the  lungs  are  suspended  in 
the  chest  to  the  upper  part  of  the  walls  of  this  cavity,  and  are 
fastened  also  to  the  spinal  column  in  the  rear.  The  large  vessels 
of  the  heart,  and  the  bronchi  of  the  lungs,  serve  as  the  princi- 


88  HUMAN  PHYSIOLOGY. 

Pleura.     Mechanism  of  breathing.    Provision  for  expansion  of  the  chest. 

pal  means  of  suspending  these  organs,  as  you  can  readily  see 
by  the  Figure.  The  lungs  are  covered  by  a  white,  shining 
membrane,  which  also  lines  the  inside  of  the  walls  of  the  chehw 
(§  67.)  called  the  pleura.  This  is  always  kept  lubricated  by 
a  watery  fluid,  so  that,  as  the  lungs  expand  and  the  chest 
moves,  the  friction  will  be  attended  with  no  inconvenience  or 
injury.  You  may  perhaps  ask  why,  as  the  lungs  follow  the 
walls  of  the  chest  in  its  expansion,  they  could  not  have  been 
fastened  to  these  walls  throughout  their  whole  surface.  The 
principal  reason  probably  is  that,  if  this  were  the  arrangement, 
the  intimate  vascular  connection,  which  would  in  this  case 
exist  between  the  walls  of  the  chest  and  the  lungs,  would  ex- 
pose the  delicate  texture  of  these  organs  more  frequently  to 
injury  from  external  violence.  As  it  is  now,  the  eifusion,  or  the 
inflammation,  consequent  upon  a  blow  on  the  chest,  is  not 
apt  to  affect  the  lung  in  the  neighborhood,  because  it  has 
no  direct  connection  with  it  by  nerves  and  blood-vessels. 

133.  You  are  now  prepared  to  see  by  what  mechanism  the 
air  is  alternately  introduced  to  and  expelled  from  the  lungs.  The 
chest  incloses  a  large  space,  which  can  be  made  much  greater  by 
certain  movements  of  its  walls.  It  is  this  expansion  of  the  cav- 
ity of  the  chest,  effected  by  certain  muscles,  which,  by  creating  a 
vacuum,  causes  the  air  to  rush  into  the  chest  through  the  tra- 
chea, just  as  air  rushes  into  the  bellows  when  the  space  within 
is  expanded  by  the  separation  of  its  walls.  That  you  may  un- 
derstand how  the  expansion  of  the  chest  is  effected,  I  now 
proceed  to  describe  the  chest.  In  Fig.  37  you  see  the  frame- 
work of  the  chest.  At  6,  6,  is  the  spinal  column,  the  grand 
pillar  supporting  the  walls  of  this  cavity.  The  ribs,  c,  c,  go 
from  this  with  a  large  curve  round  to  the  breastbone,  a,  in 
front.  The  ribs,  however,  do  not  join  directly  with  the  breast- 
bone, but  there  are  cartilages  intervening,  as  you  observe  in 
the  Figure.  The  collar-bone  goes  from  this  breastbone  across 
to  the  top  of  the  shoulder.  The  ribs  are  twelve  on  each 
side.  The  lowest  two  are  attached  only  to  the  spine,  and  are 
called  floating  ribs.  The  whole  is  so  constructed  as  to  allow  a 
very  considerable  expansion  of  the  cavity.  As,  in  effecting  this 
expansion,  the  ribs  are  carried  upward  and  forward  with  the 
breastbone,  the  ends  of  the  ribs  at  the  spine  move  but  very 
slightly.  As  the  chest  is  kept  in  constant  motion,  lightness  in 
its  walls  is  an  object  of  some  importance ;  and,  at  the  same 
time,  it  is  necessary  that  the  structure  should  be  a  strong  one, 
in  order  to  guard  effectually  the  lungs  from  injury.  Both  of 


RESPIRATION.  89 


Framework  of  the  chest.    Bones.     Cartilages.    Muscles. 


FIG.  37. 


these  objects  are  secured,  by  having  the  walls  in  front  and  at 
the  side  composed  of  so  many  bones,  well  bound  together  by 
the  muscles  which  move  them.  If  these  bones  were  all  in  one, 
it  would  be  necessary  that  it  should  be  quite  thick,  to  answer 
as  a  defence,  and  then  it  would  be  a  heavy  and  unwieldy  thing 
to  move.  The  cartilages  which  connect  the  ribs  to  the  breast- 
bone are  a  great  safeguard.  They  give  elasticity  to  the  struc- 
ture as  a  whole,  and  the  ribs  are  not  very  liable  to  be  broken, 
because  of  the  yielding  of  the  cartilages  with  which  they  are 
connected. 

134.  This  framework  is  filled  out  with  connecting  material, 
chiefly  muscles,  which  effect  the  expansion  of  the  chest  in  in- 
spiration. First,  there  is  a  large  expanse  of  muscle  and  tendon 
stretching  across  the  lower  part  of  the  chest,  separating  its  con- 
tents from  the  contents  of  the  abdomen  below.  The  edge  of  this 
muscle,  which  is  called  the  diaphragm,  is  fastened  to  the  spine 
behind,  to  the  end  of  the  breastbone  before,  and  all  around  the 
lower  ribs.  It  is  arched  upward ;  and  against  its  concave  sur- 
face press  upward  the  liver  and  stomach,  while  the  lungs  and 

8* 


90  HUMAN  PHYSIOLOGY. 

Diaphragm.     Its  action  in  inspiration  and  expiration. 


the  heart  press  downward  against  its  convex  surface.  The  dia- 
phragm is  represented  in  Pip-.  38.  The  ribs  are  cut  away  in 
front,  so  as  to  give  a  front  view  of  the  cavity  of  the  chest,  C,  c, 
the  lungs  and  heart  being  entirely  removed.  D  D  is  the 
diaphragm,  very  high  in  the  central  portion,  which  is  tendin- 
ous, but  descending  very  low  at  its  edges  at  the  sides  and  in 
the  rear. 

FIG.  38. 


DIAPHRAGM. 

Front  View. 


135.  You  can  see  that,  if  all  the  muscular  fibres  in  the  dia- 
phragm contract,  the  arch  will  be  flattened,  and  thus  the  room 
in  the  chest  will  be  enlarged.  To  occupy  this  new  room  thus 
made,  the  air  rushes  in  through  the  windpipe.  This  is  inspira- 
tion. In  expiration,  the  reverse  movement  takes  place — the 
arch  of  the  diaphragm  rises,  and,  compressing  the  lungs,  forces 
the  air  out  of  them  through  the  trachea.  In  inspiration,  as 
the  diaphragm  is  flattened,  it  pushes  down  before  it  the 
stomach,  liver,  &c.,  and  hence  the  pressing  out  of  the  abdomen, 
which  is  so  sensibly  felt,  if  the  hand  be  placed  upon  it  during 
the  act  of  inspiration.  In  expiration,  on  the  other  hand,  the 


RESPIRATION". 


91 


In  expiration  little  muscular  action.    Elasticity  the  chief  agent. 


abdomen  retreats  inward.  These  two  opposite  states  of  the 
arch  of  the  diaphragm,  and  of  the  walls  of  the  abdomen,  are 
represented  in  Fig.  39.  It  is  a  side  view,  the  ribs  being  cut 
away.  C  c  is  the  cavity  of  the  chest,  and  C  a,  the  cavity  of 
the  abdomen.  The  diaphragm  and  the  abdomen  are  represented 


FIG.  39. 


DIAPHRAGM. 

Side  View. 


as  they  are  in  expiration.  The  dotted  line  marks  the  flattening 
of  the  arch  of  the  diaphragm,  and  the  projection  of  the  ab- 
domen, as  they  occur  in  inspiration.  It  is  supposed  that  in 
ordinary  expiration,  there  is  little,  if  any,  muscular  action — 
that,  as  the  diaphragm,  which  in  inspiration  pushed  down  the 
stomach  and  liver,  and  thus  thrust  out  the  walls  of  the  ab- 
domen, ceases  to  contract  and  relaxes,  the  mere  elasticity  of 
the  parts  below,  and  especially  of  the  abdominal  walls,  restores 
the  former  condition  of  things,  and  so  the  diaphragm  is  car- 
ried upward,  and  expiration  results.  When,  however,  the  ex- 


92 


HUMAN   PHYSIOLOGY. 


Other  muscles,  besides  the  diaphragm,  act  in  inspiration. 


piration  is  at  all  forcible,  it  is  produced  in  part  by  the  action 
of  the  muscles  of  the  abdomen  and  some  of  the  muscles  about 
the  chest. 

136.  While  this  dome-shaped  muscle,  the  diaphragm,  is  the 
principal  agent  by  which  the  chest  is  enlarged,  there  are  other 
muscles  which  do  the  same  thing  in  another  way.  In  Fig.  40, 
a  is  the  spine ;  c,  c,  c,  the  ribs  ;  6,  the  breastbone ;  c?,  the  col- 
lar-bone ;  g,  the  diaphragm.  You  observe,  on  the  right  side 


c  a  h 

WALLS  OF  THE  CHEST. 

of  the  chest,  certain  muscles,  *,  extending  from  the  spinal 
column  in  the  neck  to  the  first  rib.  When  these  contract,  the 
effect  will  be  to  raise  this  first  rib,  and  all  the  others,  being 
attached  to  it,  of  course  follow.  And,  as  the  ribs,  as  you  see 
in  Fig.  37,  slant  downwards  from  the  spine  toward  the  front, 
the  result  will  be,  that  all  the  ribs  will  be  carried  together  for- 
ward and  upward.  This  result  is  the  more  effectually  secured 
by  muscles  which  pass  from  rib  to  rib,  as  seen  at  e,  e,  e,  e.  In 
this  Figure,  the  ribs,  c,  c,  c,  are  left  bare  on  the  left  side,  to  show 


RESPIRATION.  93 


Arrangement  of  muscles  between  the  ribs. 


the  arch  of  the  diaphragm,  #,  the  dotted  line  indicating  it  on 
the  right  side. 

137.  There  are  two  layers  of  muscles  connecting  the  ribs, 
the  fibres  of  which  cross  each  other,  as  represented  at  M,  in 
Fig.  41.  R  R  are  parts  of  two  ribs.  The  spaces  between  the 


FIG.  41. 


ribs  are  filled  with  muscular  fibres,  arranged  as  represented  in 
in  the  Figure.  If  the  fibres  were  straight,  as  at  L,  they  could 
not  bring  the  ribs  as  near  together  as  the  oblique  fibres  do. 
For,  as  muscles  can  not  shorten  themselves,  at  the  farthest,  more 
than  one-third  of  their  length,  the  straight  fibres  could  bring 
the  ribs  only  one-third  nearer  together,  while  it  is  obvious  that 
the  oblique  fibres,  with  the  same  contraction,  can  do  much 
more  than  that.  These  muscles  between  the  ribs  not  only, 
then,  help  to  raise  all  the  ribs  as  a  body,  as  mentioned  in  §  136, 
but  they  bring  each  rib  nearer  to  the  one  above  it.  This  in- 
creases the  expansion  of  the  chest,  especially  as  the  ribs  are  so 
joined  to  the  spine,  that  if  a  rib  be  moved  upward,  it  must  be 
carried  outward  as  well  as  forward.  You  can  see,  then,  that 
by  the  operation  of  these  muscles  in  the  neck  and  between  the 
ribs,  the  diameter  of  the  chest  will  be  increased  from  front  to 
rear,  arid  also  from  side  to  side. 

138.  The  chest  is  expanded,  then,  in  two  ways — by  flatten- 
ing the  arch  of  the  diaphragm,  and  by  raising  the  ribs.     In 
ordinary  quiet  respiration,  this  expansion  is  effected  chiefly  by 
the  diaphragm.      But  when  there  is   a  call  for  more  active 
respiration,  as  in  violent  exercise,  the  muscles  which  raise  the 
ribs  act  strongly,  and  hence  the  heaving  of  the  chest,  as  it  is 
called.     Their  action  is  violent  when  from  disease,  as  in  asthma 
for  example,  it  is  difficult  to  introduce  sufficient  air  into  the 
lungs. 

139.  The  lungs,  heart,  &c.,  accurately  fill  the  chest  in  all  the 
variations  of  size  to  which  its  cavity  is  subjected  in  respiration. 


94  HUMAN   PHYSIOLOGY. 

Change  in  the  blood  effected  in  the  air-cells. 

For,  when  the  chest  is  expanded,  the  spongy  lungs  swell  out  to 
follow  its  walls,  and  the  air  rushes  in  through  the  trachea  to 
fill  the  expanding  air-cells.  If,  now,  there  were  an  opening 
through  the  walls  of  the  chest,  communicating  with  the  out- 
side of  the  lung,  when  the  chest  expanded,  the  air  would  rush 
in  at  this  opening  as  well  as  through  the  trachea,  and  the  lung 
would  be  compressed  in  proportion  to  the  freeness  of  the  open- 
ing.  This  has  sometimes  occurred  from  disease  and  from 
wounds.  If  a  free  opening  were  made  at  the  same  time  in 
both  sides,  both  lungs  would  be  compressed,  and  death  would 
be  produced  by  suffocation,  as  really  as  if  some  obstruction  in 
the  windpipe  prevented  the  air  from  entering  the  lungs. 

140.  I  have  said  that  the  change  in  the  blood,  from  purple 
to  red,  is  effected  in  the  air-cells.     The  blood  and  the  air  are 
brought  very  near  together  for  this  purpose ;  and  yet  they  are 
kept  entirely  separate,  except  when,  from  disease,  the  blood 
escapes  into  the  air-cells  and  air-passages,  and  is  then  expecto- 
rated mingled  with  air.     It  is  supposed  that  the  air  in  the  cells 
acts  upon  the  blood  through  the  pores  of  the  vessels  containing 
it,  which  branch  out   on  the  walls  of  the  cells ;  for  if  dark 
venous  blood  be  inclosed  in  a  bladder,  the  air  will  act  through 
the  pores  of  the  bladder,  and  gradually  change  the  outer  por- 
tion of  the  blood  to  a  red  color. 

141.  These  air-vesicles,  then,  do  an  important  work.     The 
change  which  is  effected  in  them  is  immediately  essential  to  the 
continuance  of  health,  and  even  of  life.    If  the  air  be  in  any  way 
shut  out  from  them  death  occurs  at  once.     And  so  important 
is  it  that  they  should  do  their  work  well,  that  extraordinary 
provisions  are  made  to  secure  an  abundance  of  room  for  them 
under  all  circumstances.     For  the  cavity  of  the  chest,  as  you 
have  seen  in  this  chapter,  can  be  expanded  to  a  very  great  ex- 
tent.    It  would  indeed  be  difficult  to  conceive  how  a  greater 
range  of  expansion  could  be  sec^^d.      As  the  air-cells  are 
called  upon  to  do  more  work  at  some  times  than  at  others, 
there  are  special  provisions  for  a  larger  dilatation  of  the  chest 
than  is  required  in   ordinary  quiet  respiration.     Thus  when, 
from  violent  exercise,  the  blood  is  coursing  rapidly  through  the 
lungs,  and  more  air  is  therefore  needed  to  change  it  to  red 
arterial  blood,  the   chest  is  largely  expanded  by  calling  into 
action  muscles,  which  do  but  little,  if  any  thing,  in  ordinary 
breathing. 

142.  As  the  apparatus  of  res] -ration  is  so  especially  ar- 
ranged to  secure  room  for  the  lungs  under  all  circumstances, 


RESPIRATION.  95 


Injury  done  to  the  air-cells  by  compression  of  the  chest. 

it  must  be  very  deleterious  to  the  health  of  the  body  to  inter- 
fere with  this  arrangement.  If  the  expansion  of  the  chest  in 
breathing  be  limited  by  any  pressure,  every  air-cell  must  be 
embarrassed  in  doing  its  part  in  changing  the  blood.  Either 
all  of  them  must  be  unduly  contracted,  or  some  of  them  must 
become  obliterated,  so  that  there  will  not  be  as  many  vesicles 
as  there  should  be.  In  either  case,  the  organ  is  disabled  in 
proportion  to  the  amount  of  the  compression.  The  blood  is 
not  as  good  as  it  would  be  if  there  were  enough  vesicles,  and 
they  could  perform  their  work  without  constraint.  The  vigor 
of  the  system  is  therefore  lessened.  And,  besides,  the  lungs 
themselves  are  especially  liable  to  disease  from  this  unnatural 
confinement. 

143.  Much  injury  is  undoubtedly  done  to  the  lungs  that  are 
thus  confined,  when  any  strong  exercise  is  taken.     If  the  chest 
be  left  free  to  expand  to  its  fullest  extent  when  occasion  re- 
quires, this  injury  is  avoided.     For  when   the  strongly  and 
rapidly  contracting  heart  pumps  the  blood  in  such  quantities 
into  the  lungs,  the  widely  expanding  chest  draws  in  the  due 
amount  of  air  to  change  the  extra  amount  of  blood.     All  the 
air-vesicles  are  ready  to  do  their  duty,  and,  therefore,  no  violence 
is  done  to  the  delicate  texture  of  the  lungs.     But  if  these  or- 
gans be  compressed,  the  dilatation  of  those  vesicles  that  are  not 
obliterated,  in  the  midst  of  the  commotion  of  the  .difficult  res- 
piration, is  very  unequally  effected,  and  some  of  them  are 
stretched  beyond  their  proper  dimensions.     At  the  same  time, 
the  blood  must  be  here  and  there  obstructed  in  its  passage 
through  the  lungs,  producing  what  is  termed  congestion.    And 
if  this  violence  be  repeated  from  time  to  time,  permanent  dis- 
ease will  after  a  while  be  the  result. 

144.  From  the  considerations  in  the  two  last  paragraphs  it 
is  manifest,  that  the  interference  with  the  due  expansion  of  the 
lungs,  which  so  commonly  results  from  the  modes  of  dress  in 
the  female  sex,  must  be  one  of  the  prominent  causes  of  con- 
sumption, to  say  nothing  of  other  diseases  arising  from  this 
cause.     This  interference  is  effected  in  two  ways — chiefly  by 
compression  of   the  chest  directly,  but  also  by  the  pressure 
which  the  load  of  clothing  hanging  from  the  girt  waist  must 
make  upon  the  upper  part  of  the  abdomen.     This  latter  cause 
interferes  with  that  forward  movement  of  the  abdomen  which, 
as  you  saw  in  §  135,  is  necessary  to  the  flattening  of  the  arch 
of  the  diaphragm  in  the  act  of  inspiration.     The  extent  to 
which  compression  of  the  chest  is  sometimes  carried  is  seen  by 


96  HUMAN   PHYSIOLOGY. 


Change  of  the  form  and  capacity  of  the  chest  by  compression. 

comparing  the  two  outlines  in  Fig.  42.  One  is  an  outline,  of 
the  Venus  de  Medicis,  the  universally  recognized  beau  ideal 
of  beauty  of  form  in  the  female,  and  the  other  is  an  outline 


FIG.  42. 


of  the  form  of  a  lady  with  an  artificially  small  waist.  In  Fig. 
43  is  represented  the  framework  of  the  chest  of  its  natural 
size,  and  as  it  is  sometimes  contracted  by  fashion.  The  Figures 


FIG.  43. 


representing  the  contraction  of  the  chest  may  appear  at  the 
present  time  as  caricatures,  for  a  very  small  waist  is  not  con- 
sidered now  to  be  as  essential  to  beauty  in  the  female  form,  as 
it  was  twenty-five  years  ago.  The  truth,  as  uttered  by  medical 
men,  has  had  some  effect.  But  the  evil  is  remedied  only  in 


RESPIRATION.  97 


Cause  of  death  in  drowning.     Singular  provision  in  the  whale. 

part.  The  chest  of  the  female  is  still  too  much  begirt,  in  obe- 
dience to  the  tyranny  of  fashion,  to  allow  of  the  free  expan- 
sion, to  secure  which  such  special  pains  are  taken  by  nature. 
The  evil  begins  in  childhood.  The  chest  is  moulded  during 
its  growth  to  the  shape  which  fashion  prescribes.  It  could  not 
be  done  after  the  chest  has  attained  its  full  size.  The  torture 
of  the  compression  necessary  to  do  it  could  not  be  endured. 
In  childhood,  therefore,  while  the  boy's  chest  is  left  to  grow 
in  its  natural  shape  and  dimensions,  the  girl  is  begirt  so  tightly 
as  to  embarrass  her  respiration,  because  nature  is  too  ungen- 
teelly  large  in  her  patterns  to  suit  her  case.  The  subject  is 
an  important  one  ;  but  as  this  book  is  not  designed  to  treat  of 
hygiene,  I  can  not  go  into  it  further. 

145.  It  is  the  interruption  of  the  change  which  is  effected 
by  the  air  upon  the  blood  in  the  lungs,  that  produces  death  in 
drowning.  The  very  common  supposition,  that  considerable 
water  gets  into  the  lungs  in  drowning,  is  erroneous.  Very 
little  water  ordinarily  gets  in — not  enough  to  occasion  any  em- 
barrassment. The  difficulty  is,  that  the  air  is  kept  out,  and 
not  that  the  water  gets  in.  The  drowning  person  makes  at- 
tempts to  inspire,  but  the  moment  that  the  water  reaches  the 
epiglottis,  the  door  of  the  windpipe,  it  causes  at  once,  by  its 
irritation,  a  spasmodic  closure  of  the  epiglottis,  so  that  almost 
no  water  is  introduced.  In  the  mean  time,  the  purple  blood 
continues  to  be  thrown  by  the  right  ventricle  of  the  heart  into 
the  lungs.  But  the  little  air  contained  there  soon  parts  with 
its  oxygen ;  and  then  the  change  in  the  blood  ceases  to  occur, 
and  dark  blood  is  sent  from  the  lungs  to  the  heart,  and  thence 
to  all  the  organs.  These  can  not  go  on  to  do  their  duty  with- 
out the  stimulus  of  arterial  blood.  The  brain,  therefore,  gives 
out,  and  there  is  insensibility.  The  muscles  cease  to  act,  and 
all  motion  is  gone.  If  a  good  supply  of  arterial  blood  could 
be  furnished  to  all  the  organs  until  breathing  could  be  again 
commenced,  life  would  be  preserved.  And  there  is  provision 
for  such  a  supply  in  certain  animals  that  can  remain  under 
water  for  some  time.  For  example,  in  the  whale  there  are 
large  reservoirs  for  containing  arterial  blood,  which  can  be  used 
for  the  supply  of  the  organs  while  he  remains  under  water. 
"When  the  supply  begins  to  be  exhausted,  the  animal  of  course 
has  those  uncomfortable  sensations  which  a  predominance  of 
purple  blood  is  so  apt  to  produce.  He  manifests  his  uneasbess 
by  his  puffing  and  blowing,  as  he  rises  to  the  surface,  to  get  a 
fresh  supply  of  air,  and  with  it  a  fresh  supply  of  arterial  blood 
in  the  reservoirs.  9 


98  HUMAN   PHYSIOLOGY. 

Respiration  in  fishes.     Arrangement  of  the  gills. 

146.  The  apparatus  of  respiration  varies  in  different  animals, 
It  appears  in  three  forms — lungs,  gills,  and  tracheae  or  air- 
tubes.  The  gills  of  the  fish  are  arranged  in  fringed  laminae,  in 
order  to  present  by  all  its  minute  divisions  a  large  surface  ;  and 
these  delicate  organs  are  covered  with  a  lid  to  protect  them 
from  injury.  The  blood-vessels  which  contain  the  blood  to  be 
changed  branch  out  on  the  surface  of  the  fringes  of  the  lami- 
nae, just  as  the  blood-vessels  in  lungs  branch  out  on  the  surface 
of  the  air-vesicles.  The  air  which  is  to  change  it  is  mingled 
with  the  water.  It  acts  upon  the  blood,  as  the 
water  containing  it,  after  being  taken  into  the 
mouth  of  the  fish,  passes  out  through  these  la- 
minae, as  through  a  sieve.  That  the  air  in  the 
water  is  the  cause  of  the  change  can  be  proved 
by  experiment.  If  a  fish  be  placed  in  a  vessel 
with  its  orifice  closed,  so  that  no  air  can  enter,  it 
will  soon  die  from  suffocation,  because  the  air  in 
so  small  a  portion  of  water  is  soon  used  up. 
Although  the  fish  can  not  with  his  gills  use  air 
that  is  not  mingled  with  water,  it  is  supposed 
that  it  is  merely  because  the  gills  soon  become 
dry  when  exposed  to  the  air,  and  that  the  air 
would  act  on  the  blood  in  the  gills  if  they  were 
only  kept  moist.  Indeed,  in  the  land  crab,  that 
has  the  power  of  living  for  some  time  out  of  the 
water,  it  has  been  found  that  there  is  a  gland  in 
the  gill-chamber  which  furnishes  a  secretion  to 
keep"  the  gills  moist.  Gills  differ  much  in  their 
shape  and  arrangement  in  the  various  aquatic 
animals.  In  Fig.  44  is  represented  the  arenicola 
or  lob-worm.  Here,  the  gills  are  in  the  form  of 
tufts  arranged  along  the  outside  of  the  body. 
They  take  a  somewhat  similar  form  in  the  larvae 
of  many  aquatic  insects,  as  seen  in  Fig.  45.  A 
large  surface  is  presented  to  the  air  contained  in 
the  water  by  the  delicate  and  beautifully  arbor- 
escent gills  of  these  animals.  In  insects,  we  find 
the  respiration  effected  by  tracheae  or  air-tubes. 
These  go  into  all  parts  of  the  body,  and  the  air 
contained  in  them  acts  upon  the  blood  in  the  ves- 
sels which  branch  out  upon  their  walls.  The  in- 
sect, therefore,  has  no  distinct  respiratory  organs 
situated  in  any  one  part  of  the  bqdy,  but  the  LOB-WORM. 


RESPIRATION. 


99 


Respiration  in  insects.    Tracheae.     Stigmata. 


air  is  carried  into  every  part.  This  seems  to 
be  necessary  on  account  of  the  feeble  circula- 
tion in  the  insect.  The  tracheae  which,  as 
Cuvier  says,  conduct  the  air  in  search  of  the 
blood,  as  the  blood  has  no  means  of  travelling 
in  search  of  air,  open  on  the  surface  by  stig- 
mata, as  they  are  called,  which  are  of  various 
shapes  and  number  in  different  insects.  In 
the  grasshopper  there  are  twenty-four,  ar- 
ranged in  four  rows.  You  can  kill  an  insect 
by  suffocation  by  simply  covering  the  stigmata 
with  varnish.  In  Fig.  46  are  represented  the 
tracheae  in  an  insect,  the  nepa  or  water-scor- 
pion. The  tracheae,  as  you  see,  send  branches 
out  in  every  direction,  so  that  air  is  introduced 

FIG  46. 


FIG.  45. 


WING  CUT  OFF 


LARVA  OF  TUB 
MAY-FLY 


— -  AIR-SACS. 


RESPIRATORY   APPARATUS  OF  THE  WATER-SCORPIOW. 


100 


HUMAN  PHYSIOLOGY. 


Respiration  in  birds.     Apparatus  for  it  extensive. 


into  ev7ery  part  of  the  body.     There  are  lungs,  so  to  speak, 
everywhere  in  the  insect. 

147.  The  apparatus  of  respiration  is  largely  developed  in 
birds  for  two  objects — to  provide  for  the  extensive  change  in 
the  blood  which  is  required  by  their  great  activity,  and  to  give 
lightness  to  the  body.  To  secure  these  objects  there  are  air- 
sacs  connected  with  the  lungs,  and  located  in  different  parts  of 
the  body ;  and  in  birds  that  fly  rapidly  and  are  long  upon  the 
wing,  these  sacs  are  very  extensive,  and  even  many  of  the 
bones  are  made  hollow,  and  are  connected  with  the  air  sacs. 
By  this  arrangement,  the  air  is  introduced  extensively  to  the 
biood  in  the  capillaries  on  the  walls  of  these  sacs>  and  at  the 
same  time  the  body  is  made  very  light.  And  the  heat  gener- 
ated by  the  effort  of  flying  must  expand  the  air  in  the  air-sacs 
and  swell  them  out,  and  thus  make  the  body  lighter.  In  Fig.  47 
is  seen  this  arrangement  of  air-sacs  in  the  ostrich.  The  lungs, 
/,  £,  are  quite  small,  but  the  air-sacs,  c,  c,  c,  are  very  large. 
The  orifices  by  which  they  communicate  with  the  lungs  vou  see 

FIG.  47. 


LUNGS  OF  THE  OSTRICH. 


KESPIRATION.  101 


Changes  produced  in  the  air  in  the  lungs. 


in  the  Figure.  In  birds  of  great  powers  of  flight,  the  air-saca 
are  much  more  extensive.  This  arrangement  of  air-sacs  in 
different  parts  of  the  body  of  the  bird  bears  some  analogy  to  the 
tracheae  distributed  in  the  bodies  of  insects. 

148.  You  have  seen  that  the  object  of  the  apparatus  of  re- 
spiration is  to  change  venous  blood  into  arterial,  and  you  have 
also  seen  how  the  air  is  introduced  to  the  blood  in  order  to 
effect  this  change.     And  now  the  interesting  inquiry  arises, 
what  are  the  actual  changes  which  occur,  both  in  the  blood 
and  in  the  air,  in  the  lungs.      If  you  take  a  tumbler  filled 
with  lime-water,  and  breathe  into  it  through  a  tube,  the  lime- 
water  will  become  turbid,  and  will  soon  deposit  a  sediment. 
This  is  chalk,  or  carbonate  of  lime,  formed  by  the  union  of 
the  carbonic  acid  gas  exhaled  from  the  lungs  with  the  lime 
in   the   lime-water.     Whence  comes  this  carbonic  acid  gas, 
and  how  is  it  formed  ?     In  order  to  answer  this  question  satis- 
factorily, we  must  look  at  the  chemical  constitution  of  the  air 
which  we  breathe.     It  is  composed  of  two  gases,  oxygen  and 
nitrogen.     In  every  100  parts  of  common  air,  there  are  79 
parts   of  nitrogen   and  21  of  oxygen.      It   is  found  that  the 
oxygen  is  that  constituent  of  the  air  which  is  necessary  to 
life.     If  an  animal  be  placed  in  a  closed  jar  filled  with  com- 
mon air,  he  will  soon  die,  and  the  oxygen  will  be  found  to  have 
disappeared,  while  the  nitrogen  remains  very  nearly  the  same 
in  amount.     If,  now,  you  place  an  animal  in  a  jar  of  nitrogen, 
and  another  in  a  jar  of  oxygen,  the  one  in  the  nitrogen  will  die 
immediately,  while  the  other  will  be  very  lively  until  the  oxy- 
gen is  mostly  used  up  by  his  lungs.     The  animal  in  the  pure 
oxygen  will  breathe  at  first  more  rapidly  than  the  animal  in 
the  jar  of  common  air ;  and  it  is  thought  that  oxygen  is  too 
stimulating  for  the  lungs,  and  therefore  needs  to  be  diluted 
with  the  nitrogen,  as  it  is  in  the  air  that  we  breathe. 

149.  In  the  case  of  both  the  animal  in  the  jar  of  air,  and 
that  in  the  jar  of  oxygen,  carbonic  acid  is  found  to  have  taken 
the  place  of  the  oxygen  which  has  disappeared.     This  gas  is 
made  by  a  union  of  oxygen  with  carbon  or  charcoal.     It  was 
formerly  supposed  that  this  union  is  effected  in  the  lungs — • 
that  carbon  is  thrown  off  from  the  venous  blood  in  the  lungs, 
and  that  the  oxygen  of  the  air  there  unites  with  it,  and  so  car- 
bonic acid  appears  in  the  air  expired  from  the  chest.    But  it  has 
been  discovered  that  the  exchange  is  made  in  a  different  man- 
ner.    It  is  not  made  in  the  lungs.     The  oxygen  is  absorbed  by 
the  blood,  and  goes  with  it  to  the  heart  to  be  sent  all  over  the 

9* 


102  HUMAN  PHYSIOLOGY. 

Changes  produced  in  the  blood  by  the  air. 

system.  And  it  is  in  the  capillaries  that  the  oxygen  unites 
with  carbon  to  form  carbonic  acid.  The  union  takes  placa 
while  the  blood  is  changing  from  arterial  to  venous,  and  is  an 
essential  part  of  the  change.  The  carbonic  acid  thus  formed 
in  the  capillaries,  is  brought  back  to  the  heart  in  the  venous 
blood,  and  is  discharged  from  the  system  in  the  lungs.  That 
the  change  takes  place  as  stated  has  been  abundantly  proved 
in  various  ways.  It  has  been  found  by  experiments  which  I 
will  not  detail,  that  carbonic  acid  exists  in  considerable  amount 
in  venous  blood ;  while,  on  the  other  hand,  there  is  much  oxy- 
gen in  arterial  blood.  The  plain  inference  from  this  is,  that 
oxygen  unites  with  the  blood  as  it  passes  through  the  lungs, 
goes  with  it  to  the  capillaries,  and  there  unites  with  the  carbon, 
giving  us  the  carbonic  acid  which  we  find  in  the  blood  in  the 
veins,  after  it  has  passed  into  them  from  the  capillaries.  It  has 
been  found,  also,  that  if  frogs  or  other  cold-blooded  animals 
be  placed  in  hydrogen  or  nitrogen,  (gases  which  produce  no  in- 
jurious effect  on  them,)  they  will  give  off  for  some  time  nearly 
as  much  carbonic  acid  as  they  would  have  done  in  common 
air.  In  this  case,  as  no  oxygen  is  introduced  into  the  lungs, 
the  carbonic  acid  can  not  come  from  any  union  effected  in 
these  organs  between  carbon  and  oxygen,  but  it  must  be  dis- 
charged by  exhalation  from  the  blood  as  it  is  passing  through 
the  lungs.  Of  course  the  discharge  of  the  carbonic  acid  ceases 
after  a  little  time ;  for,  there  being  no  new  supply  of  oxygen  by 
way  of  the  lungs,  as  there  is  when  the  animal  is  breathing  com- 
mon air,  there  can  be  no  new  formation  of  carbonic  acid.  But 
even  cold-blooded  animals  can  not  live  in  these  gases  for  any 
great  length  of  time,  although  they  are  not  positively  deleterious 
to  them,  for  oxygen  is  needed  for  the  continuance  of  their  func- 
tions. And  in  the  warm-blooded  animals,  a  constant  supply 
of  it  is  necessary — they  will  die  if  cut  off  from  this  supply 
even  for  a  short  time. 

150.  The  change  which  takes  place  in  the  blood,  as  it  passes 
through  the  lungs,  occurs  to  some  extent  when  the  blood  is  ex- 
posed to  the  air  in  any  way.  Thus,  if  blood  be  drawn  from  a 
vein  into  a  bowl,  the  surface  of  it  becomes  red  by  the  action 
of  the  air  upon  it.  Carbonic  acid  is  discharged  from  it,  and 
the  oxygen  of  the  air  takes  its  place,  uniting  with  the  blood, 
just  as  the  process  occurs  in  the  lungs.  A  larger  part  of  the 
blood  will  be  thus  changed,  if  it  be  shaken  so  as  to  expose 
more  of  it  to  the  air.  The  change  takes  place  to  some  extent 
even  if  a  membrane  be  interposed  between,  as  when  the  blood 


KESPIKATION.  103 


Quantity  of  carbonic  acid  given  out  by  the  lungs.    Necessity  ol  ventilation. 

is  inclosed  in  a  bladder.  The  oxygen  of  the  air,  in  this 
case,  is  introduced  through  the  minute  pores  of  the  bladder, 
and  the  carbonic  acid  gas  escapes  through  them.  Precisely  in 
this  way  is  the  change  effected  in  the  lungs,  as  already  stated 
in  §  140.  The  blood  is  separated  from  the  air  by  being  con- 
fined in  blood-vessels,  and  the  air  in  the  vesicles  acts  upon  it 
through  the  minute  pores  of  these  vessels.  Arid,  as  the  blood  is 
divided  into  innumerable  little  streams,  every  part  of  it  is  acted 
upon  by  the  air  in  the  vesicles.  Though  the  texture  of  the 
lungs  is  exceedingly  delicate,  and  the  separation  between  the 
air  and  the  blood  is  almost  as  nothing,  yet  the  blood  is  confined 
to  its  limits,  even  though  it  courses  through  these  organs  with 
great,  rapidity,  and  it  never  mingles  with  the  air  except  as  9 
consequence  of  actual  disease. 

151.  The  quantity  of  carbonic  acid  gas  discharged  from  the 
lungs  in  the  course  of  twenty-four  hours  is  very  great.     Many 
experiments  have  been  tried  and  calculations  made  to  ascertain 
its -amount,  and  I  am  within  bounds  when  I  state,  that  there  is 
at  least  three-quarters  of  a  pound  of  charcoal  in  the  carbonic 
acid  thrown  off  from  the  lungs  of  a  common-sized  adult  in  the 
course  of  twenty-four  hours.      This  gas  is  a  deadly  poison. 
When  accumulated  in  a  considerable  amount,  as  when  char- 
coal is  burned  in  an  open  furnace  in  a  close  room,  it  may  prove 
immediately  destructive  to  life.     And  in  the  very  prevalent 
neglect  of  ventilation,  the  frequent  accumulation  of  this  gas 
from  the  respiration  must  prove  more  or  less  injurious  to  the 
health.     Whenever  the  proper  amount  of  oxygen  gas  is  with- 
held from  the  lungs,  and  carbonic  acid  takes  its  place,  the 
quality  of  the  blood  is  impaired  from  incompleteness  in  the 
change  effected  in  the  lungs,  and  the  vigor  of  the  body  must 
in  this  way  be  lessened,  to  say  nothing  of  the  deleterious  influ- 
ence of  this  gas  upon  the  nervous  system.     Though  the  results 
are  not  immediate  and  palpable,  great  injury  is  continually 
done  to  the  health  of  multitudes  by  the  accumulation  of  this 
gas,  in  small  close  apartments,  and  in  crowded  assemblies.     A 
congregation  of  twelve  hundred  people  in  two  hours  throw  off 
from  their  lungs  an  amount  of  carbonic  acid  that  contains 
seventy -five  pounds  of  charcoal.     And  yet  little  pains  is  com- 
monly taken  to  carry  off  this  vast  quantity  of  poisonous  gas, 
and  replace  it  with  pure  air. 

152.  As  so  much  oxygen  is  absorbed  in  the  lungs  of  all  ani- 
mals, and  so  much  carbonic  acid  is  thrown  out  from  them,  the 
inquiry  arises  how  the  air  is  replenished  with  oxygen,  and  is 


104  HUMAN  PHYSIOLOGY. 

Carbonic  acid  exhaled  from  the  lungs  of  animals  absorbed  by  plants. 

cleared  of  the  carbonic  acid  which  is  thus  so  largely  mixed  with 
it.  It  is  found  that  this  is  done,  to  a  great  extent  at  least,  by  the 
leaves  of  plants.  The  process  which  goes  on  in  these  lungs,  as 
they  may  be  called,  of  the  plants,  is  quite  the  reverse  of  that 
which  is  going  on  in  the  lungs  of  animals.  The  carbon  of  the  car- 
bonic acid  which  is  thrown  off  from  the  lungs  of  animals  is  ab- 
sorbed by  the  leaves  of  plants,  and  the  leaves  replenish  the  air 
with  the  oxygen,  which  is  so  constantly  and  abundantly  ab- 
sorbed in  the  lungs  of  the  animal  creation.  Thus,  the  animal 
and  vegetable  kingdoms  are  sources  of  supply  to  each  other. 
But  it  may  be  thought  that  there  would  be  apt  to  be  a  surplus 
of  oxygen  in  the  atmosphere  in  warm  climates,  where  the  vege- 
tation is  so  luxuriant ;  while,  on  the  other  hand,  there  would 
be  an  accumulation  of  carbonic  acid  gas  in  the  colder  regions. 
This  would  be  so,  if  the  air  were  not  so  movable  that  the  equi- 
librium is  readily  secured  in  either  case. 

153.  It  is  an  interesting  fact,  that  the  presence  of  light  is 
necessary  to  the  process  which  I  have  described  as  going  on  in 
the  leaves  of  plants.     Each  leaf  may  be  considered  as  a  labor- 
atory, and  the  light  as  the  chief  agent  in  effecting  the  chemical 
changes  that  occur  in  it.     And  it  is  found  that  no  artificial 
light  can  do  the  work.     It  is  only  the  light  of  the  sun  that  is 
competent  to  this  chemistry.    And  as  these  innumerable  labor- 
atories are  everywhere  at  work,  absorbing  the  carbon  and  ex- 
haling the  oxygen,  to  purify  the  air  rendered  noxious  by  the 
laboratories  of  the  animal  creation,  we  must  confess  it  to  be  a 
mystery  as  to  how  the  chemistry  of  the  lungs  of  animals,  and  that 
of  the  leaves  of  plants  should  be  kept  so  nicely  balanced.    The 
balance  is  so  strictly  maintained,  that  the  chemical  composition 
of  the  air  is  always  found  to  be  almost  exactly  the  same. 

154.  The  heat  of  the  body  is  maintained  by  the  union 
which  takes  place  in  the  capillaries  between  the  carbon  and 
hydrogen  of  the  system,  and  the  oxygen  which  is  introduced 
into  the  blood  through  the  lungs.     It  is  a  process  analogous  to 
combustion.     When  carbon  or  charcoal  is  burned  in  a  ves- 
sel containing  air,  the  oxygen  disappears,  for  it  unites  with 
the  carbon,  and  carbonic  acid  gas,  therefore,  appears  in  its 
place.     The  same  union  occurs  in  this  case  between  carbon  and 
oxygen,  as  we  find  occuring  in  the  capillaries.     A  sort  of  com- 
bustion, then,  is  going  on  in  every  part  of  our  bodies.     And,  as 
heat  is  evolved  in  the  one  case,  so  it  is  in  the  other.    The  same 
can  be  said  of  the  burning  of  hydrogen  and  oxygen  together. 
Heat  is  caused  by  the  union  thus  produced  between  them,  and 


RESPIRATION.  105 


Animal  heat.    Produced  by  a  sort  of  combustion.    Three  sources  of  fuel. 


so  it  is  when  they  unite  in  the  body.  The  water  which  is  ex- 
haled  from  the  lungs  comes  from  this  union  of  oxygen  and 
hydrogen.  It  was  formerly  supposed  that  the  union  between 
the  oxygen  and  the  carbon  and  hydrogen  takes  place  in  the 
lungs,  and  that  the  heat  is  made  there,  and  then  is  distributed 
over  the  whole  system.  But  it  was  objected  to  this  supposi- 
tion, that  it  made  the  lungs  a  sort  of  furnace  for  the  rest  of  the 
body,  and  that,  if  the  supposition  were  correct,  there  ought  to 
be  a  much  higher  degree  of  heat  in  these  organs  than  any- 
where else,  which  is  not  the  case.  Ingenious  theories  were 
broached  to  get  over  this  difficulty ;  but  it  was  at  length  dis- 
covered that  the  union  between  the  oxygen  and  the  carbon  and 
hydrogen  occurs  in  the  capillaries  of  the  body,  instead  of  the 
lungs,  and  that  the  combustion,  therefore,  that  produces  the 
heat  is  everywhere,  instead  of  being  in  one  locality. 

155.  The  fuel  for  this  combustion  comes  from  three  sources. 
One  of  these  is  the  waste  of  the  tissues.  This  furnishes  a  con- 
siderable amount  of  the  carbon  and  hydrogen  for  the  union 
with  the  oxygen,  in  all  animals  that  are  subjected,  from  their 
activity,  to  much  wear  and  tear  of  the  system.  I  barely  al- 
lude to  this  now,  and  shall  enlarge  upon  it  soon.  Another 
source  of  the  fuel  for  combustion  is  food.  The  oily,  sugary, 
and  starchy  kinds  of  food  are  devoted  in  a  great  measure  to 
this  particular  purpose.  These  furnish  a  sort  of  floating  fuel, 
as  we  may  express  it,  which  is  carried  about  in  the  blood. 
Hence,  we  see,  that  our  diet  must  necessarily  be  varied  accord- 
ing to  the  weather  and  the  climate.  In  cold  weather,  the  heat 
of  the  body  is  more  rapidly  abstracted  than  in  warm  weather, 
and,  therefore,  we  need  then  more  of  that  food  which  affords  a 
supply  of  carbon  and  hydrogen.  And  so  as  to  climate.  The 
enormous  quantity  of  oily  food  often  consumed  by  inhabitants 
of  very  cold  climates  is  used  up  by  being  burned,  as  we  may 
say,  in  the  capillaries  to  keep  up  the  animal  heat.  Of  course, 
keeping  the  body  warm  by  fire  and  clothing  relieves  from  the 
necessity  of  taking  any  large  quantities  of  fuel-making  food. 
Still,  under  the  most  favorable  circumstances  in  this  respect, 
there  is  a  need  of  variation  in  diet  to  suit  the  weather  and  the 
climate,  and  we  make  this  variation  for  the  most  part  instinct- 
ively. Indeed  there  is  a  marked  provision  in  nature  for  it.  I 
will  mention  but  a  single  example  of  this  provision.  While 
there  is  a  large  amount  of  fat  in  the  bears  and  seals  and  whales 
which  afford  food  for  the  Esquimaux  and  Greenlander,  there  is 
very  little  in  the  animals  which  furnish  a  part  of  the  diet  of  the 


106  HUMAN  PHYSIOLOGY. 

Animal  heat  differs  in  cold  and  warm-blooded  animals.    Why. 

inhabitants  of  tropical  climates.  Another  source,  still,  of  ani- 
mal heat  is  the  store  of  fat  which  is  laid  up  in  the  body.  Ona 
design  of  this  accumulation  of  fat  in  different  parts  of  the 
body  seems  to  be  to  provide  for  the  heat  when  other  sources 
fail.  Thus,  when  disease  destroys  the  appetite,  and  thus  cuts 
off  the  supply  of  food,  the  fat  wastes  away,  or  rather  is  burned 
up,  to  keep  up  the  temperature  of  the  body.  The  fat  is  the 
great  means  of  maintaining  the  requisite  temperature  when  hi- 
bernating animals  become  torpid  for  the  winter.  They  become 
very  fat  in  the  autumn,  before  crawling  into  their  winter  quar- 
ters, and  in  the  spring  they  come  out  very  lean,  their  fat  having 
been  consumed  in  keeping  up  the  low  degree  of  temperature  re- 
quired during  this  time. 

156.  As  the  amount  of  heat  produced,  when  charcoal  is 
burned  in  air,  or  when  oxygen  and  hydrogen  are  burned 
together,  depends  upon  the  quantities  of  carbon  and  hydrogen 
that  unite  with  the  oxygen,  so,  also,  the  degree  of  animal  heat 
depends  upon  the  quantities  of  carbon  and  hydrogen  that  unite 
with  the  oxygen  in  the  capillaries.  This  may  be  illustrated  by 
referring  to  the  effects  of  exercise  on  the  heat  of  the  body. 
When  the  circulation  is  quickened  by  exercise,  the  blood  passes 
more  rapidly  than  usual  through  the  lungs,  the  respiration  is 
consequently  quickened,  more  air  is  introduced  into  the  lungs, 
and  therefore  oxygen  is  more  rapidly  absorbed  by  the  blood. 
At  the  same  time,  the  action  of  the  muscles  effects  a  waste  in 
their  structure  by  the  wear  and  tear,  so  that  more  carbon  and 
hydrogen  are  ready  to  be  released  to  be  united  with  the  in- 
creased oxygen.  Hence  comes  the  heat  produced  by  exercise. 
So,  too,  those  animals  which  are  the  most  active,  ordinarily 
have  the  most  animal  heat,  and  have  the  most  extensive  respi- 
ratory apparatus,  so  that  there  may  be  a  free  supply  of  absorbed 
oxygen  to  unite  with  the  carbon  and  hydrogen  of  the  changing 
tissues.  It  is  in  birds  and  insects  that  this  union  takes  place 
most  largely,  and  in  them,  therefore,  the  respiratory  apparatus 
is  very  largely  developed.  This  is  to  be  attributed  to  their  mus- 
cular activity,  which  produces  so  much  waste  matter  that  must 
be  removed  from  the  system.  Cold-blooded  animals,  on  the 
other  hand,  are  very  inactive.  There  is  not,  therefore,  much 
wear  and  tear  of  the  tissues.  There  is  comparatively  little 
waste,  therefore,  to  be  thrown  off.  And  so  but  little  oxygen 
needs  to  be  introduced  into  the  lungs,  and  consequently  little 
heat  is  generated.  To  realize  fully  the  contrast  between  the 
warm  and  the  cold-blooded  animals  in  these  respects,  observe,  a* 


KESPIRATION.  107 

Uniformity  of  animal  heat  in  the  warm-blooded.     Interesting  experiments. 

the  representative  of  the  one  class,  a  canary  bird,  and  a  frog  ai 
the  representative  of  the  other.  The  frog  is  generally  quiet, 
and  only  now  and  then  takes  a  leap  or  croaks ;  but  the  bird 
is  ever  in  restless  motion,  and  sings  much  of  the  time  with 
all  his  might.  The  bird  is  warm  with  the  heat  generated  by 
the  constant  union  of  oxygen  with  carbon  and  hydrogen  in  its 
capillaries  ;  but  the  frog  is  nearly  as  cold  as  the  water  in  which 
he  is  immersed.  The  bird  breathes  rapidly,  to  let  the  oxygen 
of  the  air  largely  into  his  lungs ;  but  the  frog  scarcely  seems 
to  breathe  at  all,  so  scanty  is  the  supply  of  oxygen  which  he 
needs. 

157.  Cold-blooded  animals  are  very  nearly  of  the  same  tem- 
perature with  the  substances  that  are  around  them ;  but  warm 
blooded  animals  have  a  certain  degree  of  temperature,  which 
they  maintain  with  considerable  uniformity  under  all  variations 
of  temperature  in  the  atmosphere.  This  in  man  is  about  ninety- 
eight  degrees  of  Fahrenheit.  This,  you  observe,  is  above  the 
temperature  of  the  surrounding  air,  except  in  exceedingly  hot 
weather.  The  human  body  is  therefore  always  giving  off  heat. 
Indeed  it  is  essential  to  comfort  that  it  should  part  with  con- 
siderable heat,  for  any  near  approach  of  the  atmosphere  to 
ninety-eight  degrees  produces  an  uncomfortable  sensation  of 
heat.  But  the  amount  of  heat  which  the  human  body  can 
bear  for  a  short  time  is  much  greater  than  the  facts  above 
alluded  to  would  lead  us  to  suppose.  It  was  long  taken  for 
granted,  that  it  could  not  safely  bear,  even  for  a  short  time, 
a  heat  much  higher  than  that  which  is  endured  in  hot  climates. 
The  truth  on  this  subject  was  at  length  discovered  by  accident. 
Two  Frenchmen  were  employed  by  government,  in  1760,  to 
devise  some  method  of  destroying  an  insect  which  infested  the 
grain  at  that  time.  The  result  of  their  experiments  was  the 
discovery,  that  by  subjecting  the  grain  to  a  certain  degree  of 
heat  in  an  oven  the  insect  was  destroyed,  and  the  grain  not 
injured.  While  they  were  trying  their  experiments,  a  girl 
offered  to  go  into  the  oven  and  mark  the  height  of  the  mer- 
cury in  the  thermometer.  It  stood  at  260°  ;  and,  after  remain- 
ing there  for  ten  minutes,  which  she  found  that  she  could  do 
without  any  great  inconvenience,  she  marked  it  at  288°,  that 
is,  76°  above  the  boiling  point  of  water.  These  facts  led  to  the 
famous  experiments  of  Dr.  Fordyce  and  Sir  Charles  Blagden, 
in  England.  With  wooden  shoes,  tied  on  with  list,  they  went 
into  a  room  in  which  the  thermometer  showed  the  air  to  be 
at  260°.  Their  watch  chains  were  so  hot  that  they  could  scarcely 


108  HUMAN   PHYSIOLOGY. 


Different  degrees  of  torpor  in  hybernating  animals. 


touch  them,  and  eggs  were  roasted  hard  in  twenty  minutes,  and 
beefsteak  was  cooked  in  thirty-three  minutes.  And  yet  tha 
same  air  that  produced  these  results  was  breathed  by  them  with 
impunity,  and  it  raised  the  heat  of  the  body  but  very  little. 
The  air  which  was  breathed  out  from  the  lungs  was  so  much 
cooler  than  the  air  of  the  room,  that  it  was  refreshingly  cool  to 
the  nostrils,  and  to  the  fingers  as  they  blowed  upon  them.  In 
such  cases,  the  evil  effects  of  the  heat  are  prevented  chiefly  by 
the  great  amount  of  perspiration  that  occurs,  the  vaporization  of 
this  abstracting  the  heat,  which  would  otherwise  accumulate  in 
the  body  and  produce  disastrous  results.  The  exhalation  from 
the  lungs,  also,  has  some  influence. 

158.  In  the  state  of   hibernation,  to  which  I  have  several 
times  referred,  the  torpidity  varies  in  degree  in  different  ani- 
mals.   In  cold-blooded  animals,  respiration  and  circulation  may 
cease  altogether  in  this  state.     In  them  the  movements  of  life 
are  often,  perhaps  we  may  say  generally,  as  fully  suspended  as 
they  are  in  the  seed  that  is  kept  from  heat  and  moisture.    They 
may  be  preserved  in  this  state  for  a  long  time  and  yet  revive. 
Serpents  and  frogs  have  been  kept  in  an  ice-house  for  three 
years,  and  then  have  been  revived  on  being  brought  out  into  a 
warm  atmosphere.     In  the  warm-blooded  animals  that    hiber- 
nate the  torpidity  is  less  deep  than  in  those  which  are  cold 
blooded.     In  them  the  respiration  and  the  circulation  become 
very  slow,  but  never  entirely  cease.     Indeed  some  species  take 
food  with  them  into  their  winter  quarters,  and  occasionally  wake 
up  sufficiently  to  eat.     But  most  of  them  are  in  a  quiet,  deep 
sleep,  from  which  they  do  not  arouse  at  all  till  the  winter  is 
past.     In  this  state,  as  life  is  nearly,  sometimes  quite  at  a  stand, 
there  is  no  wear  and  tear,  and  therefore  no  change  in  the  tissues, 
and  so  there  is  no  need  of  the  introduction  of  oxygen  by  the 
respiration.     Dr.  M.  Hall,  in  his  experiments  and  observations, 
found  that  the  bat,  when  completely  torpid,  consumed  no  oxy- 
gan,  and  discharged  no  carbonic  acid  from  the  lungs,  although 
its  circulation  was  not  entirely  suspended. 

159.  The  more  active  is  the  respiration  of  animals,  the  less 
able  are  they  to  bear  a  deprivation  of  air.     A  warm-blooded 
animal  will  die  if  it  be  under  the  water  only  a  few  minutes ; 
but  a  cold-blooded  animal  can  live  under  the  water  for  some 
time,  because  it  is  not  in  so  urgent  need  of  oxygen.     And,  for 
the  same  reason,  a  warm-blooded  animal,  in  a  state  of  hiberna- 
tion, may  be  kept  under  water  for  a  long  time  without  destroy- 
ing life,  although  when  in  its  active  state  it  would  die  on  being 


FORMATION   AND   REPAIR.  109 


Formative  vessels  appended  to  the  capillaries. 

kept  under  water  for  only  a  few  minutes.  And  this  suggests  a 
probable  explanation  of  those  cases,  in  which  individuals  hava 
been  restored,  after  having  been  under  the  water  longer  than 
the  usual  time  that  suffices  to  destroy  life  in  drowning.  In  such 
cases,  the  condition  is  not  simply  that  of  a  drowned  person. 
A  blow,  or  the  shock  of  body  or  mind,  or  both,  may  have  in- 
duced a  suspension  of  active  vitality,  like  that  which  we  see  in 
the  animal  in  a  state  of  hybernation.  The  bare  fact  of  immer- 
sion in  the  water  may  have  but  little  or  even  nothing  to  do 
with  the  actual  condition.  Such  a  state  of  things  is  especially 
to  be  suspected  in  those  cases  in  which  the  countenance  does 
not  exhibit  the  usual  dark  and  full  appearance  of  drowned  per- 
sons. 

160.  I  have  thus  shown  the  extensive  play  which  the  respi- 
ration has  in  the  vital  operations  of  the  system.  I  have  shown 
what  the  chemical  changes  are,  which  it  effects  directly  in  the 
lungs,  and  indirectly  in  the  system.  And  you  have  seen  how 
the  animal  heat  is  produced  by  these  changes,  and  how  unac- 
countably it  is  so  regulated,  that  it  seldom  varies  to  any  ex- 
tent from  ite  fixed  standard.  But  it  is  to  be  remembered  that, 
while  the  lungs,  and  even  the  capillaries,  everywhere  are  thus 
chemical  laboratories,  the  nervous  system  exerts  a  constant 
influence  upon  this  chemistry  of  the  body.  This  is  especially 
seen  in  regard  to  the  production  of  heat,  but  it  is  true  of 
the  whole  range  of  the  chemical  operations.  The  laboratories 
would  all  cease  their  work  if  their  nervous  connections  were 
destroyed. 


CHAPTER  VIII. 

FORMATION  AND  REPAIR. 

161.  THE  building  and  the  repairing  of  the  various  struc- 
tures of  the  body  are  done  by  vessels  appended  to  the  capil- 
laries. The  capillaries  having  received  from  the  arteries  the 
blood,  the  building  material,  the  formative  vessels  select  from 
it,  while  it  is  in  these  capillaries,  whatever  they  need  for  their 
purposes.  The  selection  is  made  according  to  the  tissue  or 
structure  to  be  formed.  Those  vessels  which,  for  example,  form 
bone,  select  from  the  blood  very  different  constituents  from  those 
which  make  nerve  or  muscle. 

10 


110  HUMAN   PHYSIOLOGY. 


Selecting  power  of  the  formative  vessels.     Their  concert  of  action. 

162.  It  is  wonderful  that  the  blood  can  be  formed  from  such 
a  variety  of  food  as  is  often  taken  into  the  stomach.     But  it  is 
far  more  wonderful  that  from  the  blood  can  be  made  so  many 
and  such  different  structures.    How  different  are  the  teeth  from 
the  gums  which  surround  them  ;  and  yet  both  are  made  from 
the  blood.     Observe,  in  some  particular  part  of  the  body,  how 
many  different  structures  there  are  which  are  all  made  from  the 
same  common  material.     Take,  for  example,  those  which  are 
in  and  around  the  eye.    There  are,  the  skin  of  the  eyelids ;  the 
eyelashes ;  the  vascular  lining  on  the  inside  of  the  lids ;  the 
cartilages  of  the  lids ;  the  firm,  white  coat  of  the  eye,  giving 
to  the  eyeball   its  firmness ;  the  thin,  transparent  window  in 
front,  setting  into  the  firm,  white  coat,  like  a  watch-glass  into 
the  case ;  the  beautiful  iris,  a  round  moving  curtain  with  a  cen- 
tral opening ;  the  lens  behind  this  opening ;  the  optic  nerve  ex- 
panded on  the  inside  of  the  cavity  of  the  eye ;  the  muscles 
that  move  the  eye,  with  their  tendons;  the  tear-gland;   the 
cushion  of  fat  on  which  the  eye  reposes ;  the  bone  which  forms 
the  socket,  &c.     All  these  various  textures  are  formed  from  the 
blood  ;  and  the  different  workmen  are  as  unerring  in  their  se- 
lections from  this  common  material,  as  if  they  were  intelligent 
beings.     Indeed,  no  ordinary  intelligence  could  accomplish  such 
a  selection.     It  is  effected,  inscrutably  to  us,  under  the  direction 
of  an  all-wise  Intelligence,  and  by  Almighty  power. 

163.  But  these  builders  of  the  body  not  only  have  the  power 
of  selecting  their  building  materials  from  the  blood,  but  they 
work  in  concert.     Each  company  of  builders  work  together  in 
harmony,   as    if  they  were   under   intelligent   leaders.      And 
though  different  companies  may  be  in  close  proximity,  there  is 
no  disagreement  nor  interference.     For  example,  the  builders 
of  a  tooth  and  the  builders  of  the  gum  around  it,  do  not  en- 
croach on  each  other ;  but  each  do  their  appropriate  work  with- 
in their  assigned  limits.     Even  when  different  structures  are 
intermingled,  as  when  tendon  and  muscle  mingle  together  at 
their  place  of  union,  there  is  no  confusion-  in  the  work  of  the 
two  sets  of  laborers.    In  Fig.  48  you  see  the  difference  in  struc- 
ture between  the  transparent  cornea  in  the  front  part  of  the 
eye  and  the  white  coat,  the  sclerotic  coat,  into  which  the  cornea 
is  set  like  the  crystal  of  a  watch.     It  is  represented  as  seen 
magnified   320   times.     The  dotted  lines   mark  the  place  of 
union.     The  cornea,  a,  is  a  much  more  open  structure,  you  ob- 
serve, than  the  sclerotic  coat,  b.     The  builders  of  these  two 
structures,  though  some  of  them  are  in  such  near  neighborhood 


FORMATION   AND   REPAIR. 


Concert  of  action  shown  in  producing  different  shapes. 


FIG.  48. 


never  encroach  on  each  other,  but  each  set  adheres  strictly  to 
its  own  kind  of  work.  The  sclerotica-makers  never  go  to  mak- 
ing the  open  work  which  you  see  in  the  cornea.  If  they  should 
do  so  at  any  point  there  would  be  a  little  transparent  window 
at  that  point  in  the  white  of  the  eye  ;  and  if  the  cornea-makers 
should  at  any  point  make  close  work  like  that  in  the  sclerotica, 
here  would  be  a  white  spot  in  the  cornea. 

164.  The  concert  of  action  which  we  observe  in  the  different 
sets  of  formative  vessels  is  to  be  looked  at  in  another  point  of 
view.     It  is  such  that  they  give  a  definite  and  peculiar  shape  to 
the  structure  which  they  make.     Each  bone  differs  in   shape 
from  every  other  bone,  each  muscle  from  every  other  muscle  ; 
and  so  of  other  parts.     There  is  very  great  variety  of  shape  in 
the  structures  of  the  body  ;  and  each  shape  can  be  determined 
only  by  a  certain  concert  among  the  builders.     That  you  may 
realize  in  some   measure   the  extent  of  this  variety,  observe 
again  the  numerous  different  textures  which  I  have  mentioned 
as  making  up  the  eye.     Each  of  these  has  its  own  peculiar 
shape,  and  its  definite  limits.     Its  builders  work  after  a  fixed 
plan,  and  within  fixed  bounds. 

165.  This  concert  of  action  may  be  looked  at  in  still  another 
point  of  view.     If  the   different  structures  in  the  body  were 
made,  as  a  crystal  is,  by  layer  after  layer  of  particles  deposited 
upon  the  outside,  wonderful  as  the  concert  among  the  little 
builders  would  be  in  that  case,  it  would  not  be  any  thing  like 
as  wonderful  as  it  is  now.     In  the  growth,  that  is  the  construc- 
tion of  any  part,  the  addition  is  made  by  the  formative  vessels  at 
every  point  of  the  part,  and  not  upon  the  outside  merely.     As 
these  builders  are   at  work  enlarging  the  part  in  the  growth 
from  infancy  to  childhood,  they  must  so  act  in  concert,  as  to 


112  HUMAN   PHYSIOLOGY. 

Change  of  action.    The  teeth.    Tadpole  and  frog. 

preserve  the  same  general  form  in  the  part  during  all  the  suc- 
cessive stages  of  growth.  And,  as  all  the  different  stiuctures 
of  the  body  enlarge  together,  there  must  be  agreement  between 
different  sets  ;  else  there  would  be  encroachment  and  confusion. 
Thus  in  the  growth  of  the  tiny  arm  of  infancy  to  the  sturdy 
arm  of  manhood,  each  set  of  builders  must  during  all  this  time 
keep  within  its  proper  limits,  so  that  there  may  be  just  the  right 
proportion,  and  the  right  position  of  bone,  and  muscle,  and 
tendon,  and  ligament,  and  cellular  membrane,  and  skin,  and 
nail,  &c.,  that  make  up  the  arm. 

166.  But  this  concert  of  action  appears  the  most  wonderful 
when  a  new  action,  or  change  of  action  is  called  for.     In  the 
transition  from  childhood  to  youth,  for  example,  the  builders 
of  the  apparatus  of  the  voice,  the  larynx,  all  at  once  become 
unusually  active  in  their  work,  and  a  great  enlargement  of  this 
musical  instrument,  for  such  it  is,  takes  place,  so  that  it  may 
now  utter  the  grave  notes  of  manhood.     Soon,  too,  the  beard- 
builders  begin  their  new  work  upon  the  face.     And  during  the 
period  of  childhood  new  operations  have  been  continually  insti- 
tuted  among  the    builders   of  the  teeth,  as  one  tooth   after 
another  has  made  its  appearance,  and  as  the  new  set  have  re- 
placed the  old.     To  produce  in  the  enlarging  jaw  a  new  set  of 
teeth  to  take  the  place  of  the  smaller  and  less  numerous  first 
set,  and  to  bring  them  out  in  a  symmetrical  arrangement,  re- 
quire a  very  complicated  series  of  operations.     To  effect  each 
one  of  these,  there  must  be  concert  of  action  among  the  forma- 
tive vessels ;  aiid   there   must  be   a   most  wonderful    concert 
among  the    different    successive    sets    of   builders,  to  make 
all  tliese  series  of  operations  work  out  at  length  the  general 
result. 

167.  This   change   of  action    in    the   formative    vessels   is 
strikingly  exemplified  in  some  animals.     I  refer  to  those  that 
so  entirely  change  their  forms  during  the  period  of  their  exist- 
ence.    I  will  give   two  examples.     The    first  is   the   common 
frog.     He  is  at  first  what  is  termed  a  tadpole,  and  goes  through 
many  successive  changes  to   become  a  complete  frog.     Tliese 
changes  are  represented  in  the  following  figures.     The  relative 
sizes  are  not  preserved,  the  tadpole  state  being  represented  re- 
latively much  too   large,  for   the  purpose    of  showing    more 
clearly  the  development  of  the  legs.     The  young  tadpole  is 
represented  in  Fig.  49.     It  has   a  large  head  and  body,  and  a 
long  flat  tail  by  which  it  swims  easily.     There  are  no  promi- 
nences to  indicate  the  putting  forth  of  any  thing  like  limbs.     It 


FORMATION   AND   REPAIR. 


113 


Change  of  action  in  the  silk-worm.     Concert  preserved  in  these  cases. 

FIG.  50. 


has  gills,  which  are  loose  fringes  on  each  side  of  the  head. 
These  gills  after  a  time  disappear,  and  it  has  another  set  of 
gills  arranged  under  a  fold  of  skin  very  much  like  the  gills  of  a 
fish.  The  form  is  then  as  in  Fig.  50.  The  next  change  is 
this.  The  hind  legs  begin  to  grow  out  as  seen  in  Fig.  51. 
Next,  the  fore  legs  appear  as  seen  in  Fig.  52.  The  tail  is  still 
very  large.  This  now  gradually  disappears  while  the  legs  grow 
as  represented  in  Fig.  53.  In  Fig.  54,  representing  the  perfect 
frog,  the  tail  has  entirely  disappeared.  With  these  exterior 
changes  interior  ones  have  been  going  on  also.  The  animal, 
which  was  at  the  first  a  real  fish,  breathing  with  gills 
and  swimming  in  water,  has  lost  its  gills,  and  has  now  a  pair 
of  lungs  ;  and  it  is  no  longer  able  to  remain  long  under  water, 
without  coming  to  the  surface  to  breathe  the  air. 

168.  The  other  example  is  the  silk- worm.  It  is  represented 
in  Fig.  55.  When  it  has  attained  its  full  growth,  it  passes  into 
what  is  termed  its  chrysalis  state,  Fig.  56,  it  having  previously 
woven  for  itself  from  its  silken  thread  a  case  or  cocoon. 
While  it  is  in  this  state  of  inactivity  great  changes  are  going 
on  in  its  structure,  and  it  at  length  becomes  a  perfect  winged 
insect,  as  represented  in  Fig.  57. 

In  the  two  cases  which  I  have  described,  in  each  successive 
change,  the  concert  of  action  in  the  formative  vessels  is  pre- 
10* 


114 


HUMAN   PHYSIOLOGY. 


Change  of  action  to  meet  new  exigencies. 


served,  but  it  is  after  a  new  plan.     This  change  of  plan  makei 
the  concert  of  action  exceedingly  wonderful. 

FIG.  55.  FIG.  56. 


FIG.  57. 


169.  The  change  of  action  in  the  formative  vessels,  which  is 
sometimes  called  for  by  accident  and  disease,  exhibits  in  an  in- 
teresting  manner   the   concert   between    these   vessels   as   in- 
fluenced  by  circumstances.     When  a    bone  is    broken,    these 
formative  vessels  set  themselves  to  work  to  repair  the  injury, 
by  forming  new  bone  between   and  around  the  two  ends  of 
bone,  which  new  bone  we  call  callus.     In  this  case,  the  bone- 
builders  extend  their   range  of  operations    to    meet  the    new 
necessity  ;    and  in  doing  so  they  maintain  the  same  concert 
which    marked   their    usual    operations    before  the    bone    was 
broken.     I    stated  in  §  105,  that  when  an  artery  is  tied,    to 
cure  an  aneurism,  the  circulation  in  the  limb  is  kept  up  by  the 
small  arteries  that  go  off  from  it  above  the  ligature,  communi- 
cating with  those  that  branch  off  below ;  and  that,  in  order  to 
make  the    circulation    perfect,    some  of  these  communicating 
arteries  gradually  enlarge,  to  meet  the  necessities   of  the  case 
Now,  this  enlargement  is  not  a  mere  dilatation  produced  tr- 
ibe distending  blood.     The  arteries  grow  in  thickness  as  wel. 
as  in  capacity.     The  artery-builders  are  awakened  to  a  new  ac- 
tivity, and  make  the  arteries  in  this  quarter  after  a  larger  pat- 
tern than  the  one  originally  designed  for  them. 

170.  Concert  of  action  under  successive  changes  is  strikingly 
exhibited  in  the  processes  of  inflammation.     The  following  ac- 
count of  these  processes   is  from  a  work    published    by  the 
author,  entitled  "  Physician  and  Patient."     "  You  see  a  swelling. 


FORMATION   AND   REPAIR.  115 

Illustration  from  processes  of  inflammation. 

It  after  a  while  begins  to  soften.  There  is  matter  in  it,  but  it 
is  not  yet  very  near  the  surface.  But  soon,  at  some  point,  it 
comes  nearer  and  nearer  to  the  surface,  the  wall  of  the  abscess 
thus  becoming  constantly  more  thin,  till,  at  length,  it  opens 
and  discharges.  The  discharge  continues  till  the  swelling  is 
nearly  all  gone,  and  the  remainder  is  absorbed,  and  the  part 
is  restored  to  its  natural  state.  Just  look  for  a  moment  at 
the  complicated  character  of  this  apparently  simple  operation. 
Here  is  quite  a  large  deposition  of  substance  which  is  to  be  re- 
moved; and  this  is  the  object  to  be  effected.  Observe  how  it 
is  done.  The  softening  of  the  swelling  is  not  a  mere  change 
of  solid  substance  into  a  fluid,  as  if  by  decay,  but  it  is  the  re- 
sult of  an  active  process,  which  we  call  suppuration.  When 
this  process  is  properly  performed  good  pus  is  made,  or  as 
the  old  writers  in  medicine  rather  quaintly  expressed  it,  laud- 
able pus.  This  process  of  suppuration,  when  it  is  well  done, 
does  not  go  on  here  and  there  in  the  swelling,  making  it  like  a 
honeycomb  with  a  multitude  of  little  abscesses ;  but  there  is  a 
consent,  an  agreement  of  action  by  the  vessels  of  the  part,  as 
really  as  if  they  worked  intelligently.  It  is  this  consent 
of  action  which  not  only  makes  the  line  of  movement 
in  the  abscess,  but  points  it  towards  the  surface,  instead  of 
giving  it  some  other  direction,  laterally  or  inward,  upon  some 
of  the  internal  organs.  But  it  is  further  to  be  observed,  that 
in  this  agreement  of  action,  the  vessels  of  the  part  do  not  all  do 
one  thing.  Three  different  offices  are  performed  by  them  in 
the  different  quarters  of  the  abscess.  While  some  of  these 
little  workmen  are  forming  the  pus,  there  are  others  thinning 
the  wall  of  the  abscess  in  the  direction  of  the  surface,  by 
absorbing  or  taking  up  the  substance  there ;  while  there  are 
others  still,  in  the  rear,  and  at  the  sides  of  the  abscess,  deposit- 
ing substance,  in  order  to  make  a  barrier  to  prevent  the  pus 
from  being  diffused  in  the  surrounding  parts.  Each  class  of 
these  workmen  perform  their  particular  work  with  even  more 
exactness  and  harmony,  than  would  be  expected  of  any  com- 
pany of  intelligent  laborers  under  the  direction  of  a  leader. 
The  absorbents  absorb  together,  the  wall-builders  build  together, 
and  the  makers  of  pus  make  pus  together,  and  deposit  it  in  a 
common  reservoir. 

171.  But  observe  farther,  and  you  will  soon  see  an  entire 
change  come  over  the  whole  scene  of  operations.  When  the 
absorbents  have  completed  their  passage  for  the  pus  through 
the  skin,  the  pus  is  gradually  discharged  from  its  reservoir,  and 


116  HUMAN   PHYSIOLOGY. 

Formative  vessels  and  absorbents  act  in  concert. 

the  "  occupation  "  of  the  pus-makers  is  soon  "  gone."  The  wall 
builders  also  cease  their  work,  and  while  the  vacancy  becomes 
filled  up  by  contraction  and  deposition,  the  wall  of  defense,  so 
carefully  maintained  so  long  as  was  needed,  is  now  taken  up 
by  the  absorbents,  workmen  which  seem  to  know  just  when,  as 
well  as  how,  to  do  their  duty." 

172.  Here   you   have   concert   of  action  exemplified   in   a 
complicated  set  of  associated  actions,  to  accomplish  a  tempo- 
rary   purpose.      These    actions,    as   you    see,    change   in   the 
different  stages  of  the  process,  each  one  being  performed  just  at 
the  time,  and  during  the  period  that  it  is  wanted.     And  when 
the  temporary  purpose  aimed  at  is  accomplished,  the  vessels  of 
the  part  resume  at  once  their  ordinary  duties.     It  is  to  be  ob- 
served also,  that  the  concert  of  action  is  not  confined  to  the 
formative  vessels ;  but  it  appears  also  in  those  vessels  called 
absorbents,    of  which  I   shall   speak   soon   more  particularly. 
And  these  two  sets  of  vessels  do  not  interfere  with  each  other, 
but  have  a  sort  of  agreement  together  in  accomplishing  the 
general  result.     This  concert  of  action  is  plainly  seen  among 
the  absorbents,  not  only  in  this  case,  but  in  all  the  cases  that  I 
have  cited  as  exhibiting  it  among  the  formative  vessels.     For 
example,  in  the  case  of  the  frog   (§  167)  while  the  formative 
vessels  are   constructing  the  legs,  the  absorbents  are  removing 
the   tail.     So  in  the    case    of  the  teeth    (§  166)  while    the 
formative  vessels  are  constructing  the  second  set,  the  absorbents 
remove  the  ends  of  the  fangs  of  the  teeth  in   the  first  set,  so 
that  they  are  loosened  in  their  sockets,  and  are  thus  taken  out 
of  the  way  of  the  coming  teeth.     And  indeed,  wherever  there 
is  formation,  there   is  absorption ;  and  the   same   concert  of 
action  always  appears. 

173.  I  have  spoken  of  the  great  variety  of  structures,  which 
are  made  out  of  the  same  material,  the  blood.     Besides  this, 
all  the  different  secretions   are   also  formed  from   the   same 
material.     This  appears  wonderful  when  we  look  at  the  differ- 
ence between  such  secretions  as  the  tears,  the  ear-wax,  the 
gastric  juice,  the  bile,  <fec.     And  it  appears  more  wonderful  still, 
when  we  consider  that  these  various  glands,  or  factories,  as  we 
may  call  them,  are  built  from  the  same  material  out  of  which 
they  make  their  products.     There  is  one  curious  exception  to 
this.     It  is  in   the  case  of  that  large  gland,  the   liver.     This 
gland  is  built  {.nd  kept  in  repair,  like  all  the  other  glands,  by 
arterial  blood.     But  while  they  make  their  secretions   out  of 
this  arterial  blood,  the  liver  makes  its  secretion  out  of  venous* 


FORMATION  AND  REPAIR.  117 

Formation  of  all  parts  from  the  blood.     Waste.     Lymphatics. 

blood,  which  is  brought  to  it  for  that  purpose  as  described  in 
§108. 

174.  Thus,  all  *he  solids  and  fluids  in  the  body  are  made 
from  the  blood.     Even  the  heart  itself  is  made  from  the  blood 
which  it  pumps  out  into  the  aorta ;  for  from  this  aorta  go  out 
some  small  arteries,  to  carry  blood  to  the  walls  of  the  heart  for 
its   growth   and   repair.       These    arteries   are   represented   in 
Fig.  31. 

175.  There  is  not  only  construction  going  on  in  every  part 
of  the  system,  but  there  is  waste  also.     The  wear  and  tear  of 
the  ever-moving  machinery  continually  makes  some  of  the  par- 
ticles useless,  and  these  must  in  some  way  be  removed.     I  pro- 
pose now  to  show  how  this  is  done. 

176.  There  are  two  kinds  of  waste  particles;  and  for  the  dis- 
posal of  them  two  different  plans   are  pursued.     Some  of  the 
waste  particles,  though  wholly  useless  where  they  are,  can  be 
rendered  tit  to  be  used  again  by  being  subjected  to  certain  pro- 
cesses.    These,  therefore,  are  not  thrown  out  of  the  system,  but 
are  taken  up  by  absorbents,  and  are  carried  where  the  neces- 
sary processes  can  be  applied  to  them ;  and  then  they  are  in- 
troduced into  the  blood,  to  make  again  a  part  of  the  building 
material.     But  there  are  some  waste  particles  that  can  not  be 
used  again  ;  and  these  are  so  managed  as  to  be  got  rid  of  at 
various  outlets  of  the  system.     These  two  kinds  of  particles  are 
taken  up  by  two  different  sets  of  absorbents.     The  selecting 
power  which  they  thus  exert  is  as  unerring  as  if  they  were  pos- 
sessed of  intelligence  ;  and  it  is  wholly  unaccountable,  although 
some  physiologists  have  attempted  to  explain  it. 

177.  The  particles  which  can  be  used  again  are  taken  up  by 
absorbents,  which  are  termed  lymphatics.     These  vessels  are 
much  like  the   lacteals,  the  absorbents  in  the  intestines.     They 
unite  together,  as  they  come  from  all  parts  of  the  body,  into 
two  trunks.     One  of  these  is  the  thoracic  duct  (described  in 
§91),    which  is  the  common  duct,   both  of  the   lymphatics 
and  the  lacteals,  (Fig.  17,)  and  in  which  the  chyle  and  the 
lymph,  as  the  fluid  in  the  lymphatics  is  called,  are  mingled  to- 
gether.    The  other  trunk,  which  receives  the  lymph  from  but  a 
small  part  of  the  body  empties  its  contents  into  a  large  vein  at 
the  right  side  of  the  top  of  the  chest.     The  largest  part  of  the 
lymph,  therefore,  unites  with  the  chyle,  and  is  poured  with  it 
into  the  circulation,  and  the  rest  reaches  the  same  destination 
by  another  way.     It  all  becomes  with  the  chyle  a  part  of  the 
blood.     But  before  this  is  done  it  passes,  like  the  chyle,  through 


118  HUMAN  PHYSIOLOGY. 

Two  kinds  of  waste  particles.     Excretion  and  secretion.  . 

glands,  in  order  to  fit  it  to  become  again  a  part  of  the  building- 
material  of  the  body.  These  glands  are  every  where  in  the 
track  of  the  lymphatics.  They  are  often  enlarged  from  disease, 
and  then  they  can  be  readily  felt.  This  is  often  the  case  with 
these  glands  in  the  neck.  In  relation  to  this  appropriation  of 
waste  particles,  which  I  have  thus  described,  it  may  be  truly 
said  that  man  lives  in  part  upon  his  own  flesh. 

178.  Those  waste  particles  which  are   entirely  useless  are 
taken  up  by  the  veins  directly  into  the  circulation.     They  then 
travel  the  rounds  with  the  blood,  and  are  thrown  off  from  the 
system  by  organs  appropriated  for  that  purpose.     These  organs 
are  the  lungs,  the  skin,   the  liver,  the  kidneys,  <fec.     Each  of 
these  excretory  organs  is  fitted  to  throw  off  its  particular  part 
of  the  waste.     Thus  the  lungs,  excrete  a  kind  different  from 
that  which  the  skin  does ;  and  so  of  the  rest.     The  lungs,  as 
you  saw  in  the  chapter  on  respiration,  throw  off  in  the  form  of 
carbonic  acid  gas,  large  quantities  of  the  carbon  evolved  in  the 
wear  and  tear  of  the  system.     The  liver,  the  skin,  &c.  throw 
off  parts  of  the  waste  which  differ  from  that  which  is  thrown 
off  by  the  lungs.     Why  it  is  that  the  waste  matter  is  thus  in- 
troduced into  the  circulation  to  be  carried  to  the  excretory  or- 
gans, instead   of  having  special  channels  appropriated  to  the 
particular  office  of  carrying  it  to  its  outlets,  we  know  not.     And 
how  it  can  thus  be  mixed  with  the  blood,  and  be  carried  about 
the  system  without  proving  noxious,  is  a  mystery.     That  it  can- 
not be  long  retained  in  the  blood  without  doing  injury,  is  shown 
by  the  evil  results,  which  come  from  a  suspension  of  excretion 
from  any  of  the  organs  that  I  have  mentioned. 

179.  It  is  interesting  to  observe  that  some  of  the  excretory 
organs  perform  other  functions  besides  that  of  mere  excretion.* 
Thus  the  lungs,   while  they  excrete  carbon,    absorb  oxygen, 
without  which  life  could  not  go  on.     At  the  same  time,  too, 
they  act  as  the  bellows  for  the  organ  of  the  voice,  the  larynx, 
as  you  will  see  in  the  chapter  on  that  subject.     So  also,  the 
liver,  while  it  excretes  what  would  be  noxious  if  it  remained  in 
the  blood,  puts  its  excretion  into  such  a  form,  that  it  proves,  as 
you  saw  in  the  chapter  on  digestion,  an  auxiliary  in  some  of 
the  processes  of  the  digestive  organs. 

*  The  words  excretion  and  secretion,  are  often  applied  to  the  same  thing.  Excretion, 
rtrictly  speaking,  should  be  applied  only  to  something  to  be  thrown  off,  and  not  to  some- 
thing formed  to  be  used.  But  sometimes  an  excretion  is  so  formed,  that  it  can  be  used, 
and  then  the  word  secretion  is  also  applicable  to  it.  Thus  the  bile,  while  it  is  an  ex- 
cretion containing  noxious  particles  to  be  thrown  off  from  the  system,  is  put  to  use 
and  so  it  is  as  often  called  a  secretion  as  an  excretion. 


FORMATION   AND   REPAIR. 


119 


The  skin.     Cuticle.     True  skin.     Papillae. 


FIG.  58. 


180.  The  skin,  while  it  is  an  extensive  excreting  organ,  per- 
forms other  important  offices.  It  serves  as  a  firm  yet  very 
flexible  and  soft  covering  to  the  body,  protecting  its  internal 
parts  from  injury.  It  is  highly  endowed  with  nerves  for  two  pur- 
poses— the  one,  that  it  may  act  as  a  sentinel  to  warn  of  danger ; 
and  the  other,  that  it  may  be  the  seat  of  the  sense  of  touch. 
That  you  may  see  how  well  it  is  fitted 
to  perform  these  various  functions, 
I  will  describe  here  its  structure. 
What  is  very  commonly  spoken  of  as 
the  skin,  is  not  really  the  skin,  but 
only  a  covering  for  it.  When  the 
skin  is  rubbed  off,  as  it  is  expressed, 
it  is  only  this  covering  of  the  skin,  or 
cuticle,  which  is  removed.  The  skin 
which  is  raised  by  a  blister  is  this  cu- 
ticle. The  great  object  of  the  cuticle 
is  to  protect  the  true  skin,  which  is 
very  highly  endowed  with  nerves  for 
the  purposes  mentioned  above,  and 
which  therefore,  if  uncovered,  would 
prove  a  source  of  severe  suffering.  As 
it  is,  the  cuticle  protects  the  skin  effec- 
tually, and  yet  does  not  interfere  with 
its  functions  as  the  organ  of  the  sense 
of  touch.  It  is  of  so  slight  and  so 
soft  a  texture,  that  the  nerves  of  touch 
may  readily  receive  impressions 
through  it.  It  is  composed,  as  you 
will  see  in  the  next  chapter,  of  many 
layers  of  minute  round  cells,  the 
outermost  layers  being  made  up  of 
these  cells  broken,  and  emptied  of  the 
fluid  which  they  contained.  The 
true  skin,  which  the  cuticle  covers,  is 
of  a  fibrous  texture,  with  a  good 
supply  of  both  nerves  and  blood  ves- 
sels. On  the  surface  of  this  true  skin 
next  to  the  cuticle  are  eminences  called 
papillae.  In  these  are  seated  the  ex- 
tremities of  the  nerves  of  touch. 
Fig.  58  'represents  a  highly  magni-  Vertical  section  ofthe 

fied  section  of  a  bit  of  the  skin  from  SOLE  OF  THE  FOOT. 


120  HUMAN   PHYSIOLOGY. 


Tubing  in  the  skin.     Insensible  perspiration.     Sebaceous  glands. 

the  sole  of  the  foot ;  a  is  the  cuticle ;  c  is  the  true  skin ;  b  re- 
presents the  papillae.  You  observe  that  the  deepest  layers  of 
the  cuticle,  next  to  these  papillae,  are  more  colored  than  the 
outer  ones.  The  coloring  matter  of  the  skin  is  situated  here. 
You  observe  also  a  tube  which  runs  up  through  the  cutis  or 
true  skin  and  the  cuticle,  and  in  the  latter  part  of  its  course 
has  a  sort  of  cork-screw  arrangement.  This  is  the  discharging 
tube  of  the  sweat-gland,  d,  lying  within  the  true  skin,  and  sur- 
rounded with  globules  of  fat.  These  glands  are  more  numer- 
ous in  some  parts  of  the  skin  than  in  others.  They  are  par- 
ticularly numerous  on  the  palms  of  the  hands,  and  on  the  soles 
of  the  feet.  Mr.  E.  Wilson  counted,  with  the  aid  of  the  mi- 
croscope, 3528  of  them  in  a  square  inch  on  the  palm  of  the 
hand.  Reckoning  the  length  of  one  of  these  at  one  quarter  of 
an  inch  it  gives  882  inches  or  73£  feet  of  tubing  in  this  small 
space.  He  calculated  the  amount  of  this  tubing  in  the  skin  of 
the  whole  body  as  being  48,600  yards,  or  nearly  28  miles. 
The  amount  of  excretion  from  the  seven  millions  of  these  tubes, 
which  open  on  the  surface  of  the  skin,  is  very  great.  Many 
experiments  have  been  tried  to  determine  what  the  amount 
is  in  24  hours,  but  approximations  only  to  the  truth,  of  course, 
could  be  obtained,  and  the  results  of  the  experiments  have 
differed  much.  While  the  excretion  is  great  in  amount,  it  is 
very  important.  It  is,  as  you  have  seen  in  the  chapter  on 
Respiration,  a  great  means  of  regulating  the  temperature  of 
the  body.  It  is  also  the  means  of  discharging  from  the  body 
a  portion  of  its  waste.  This  waste  is  dissolved  in  or  mingled 
with  the  water  or  vapor  of  the  perspiration.  The  perspira- 
tion is  ordinarily  insensible,  as  it  is  termed  ;  that  is,  it  is  in  the 
form  of  vapor.  But  sometimes,  as  in  vigorous  exercise,  when 
the  sweat  glands  are  rendered  very  active,  chiefly  to  prevent  too 
great  an  accumulation  of  heat,  the  perspiration  becomes  sensible. 
181.  There  is  another  set  of  glands  in  the  skin  called 
sebaceous  glands,  which  secrete  an  oily  fluid.  They  have 
also  thin  "tubes  like  the  sweat  glands.  They  are  most 
abundant  where  the  skin  specially  needs  an  oily  lubrica- 
tion, as  where  there  are  folds  in  the  skin  or  hairs,  or 
where  the  skin  is  exposed  to  friction,  or  to  the  drying  atmos- 
phere. They  are  very  abundant  on  the  face  and  head.  The 
amount  of  the  oily  secretion  of  these  glands  is  very  great  in 
the  skin  of  races  fitted  to  inhabit  warm  climates.  Every  hair 
has  sebaceous  glands  connected  with  it,  as  represented  in 
Fig.  59  ;  in  which  6  is  the  hair  emerging  from  the  skin ; 


FORMATION   AND   REPAIR. 


121 


Influence  of  labor  on  wear  and  tear,  and  on  absorption. 


HAIR 

and  sebaceous  glands. 


a  a  are  the  sebaceous  glands  pouring  their 
secretion  by  thin  tubes  into  the  tube  or 
canal  in  which  the  hair  grows  ;  c  the  root 
of  the  hair  surrounded  with  fat  globules. 
From  all  this  you  see  that  the  skin,  with 
its  two  sets  of  glands  and  tubes,  its  nerv- 
ous papillae,  and  its  layers  of  constantly 
renewed  cells,  making  the  cuticle,  is  a 
complicated  organ,  and  is  thus  fitted  to 
perform  its  functions  as  an  organ  of  sen- 
sation, and  at  the  same  time  of  excretion, 
while  it  is  also  a  pliable  but  firm  cover- 
ing for  the  body. 

182.  You  have  seen  in  the  facts  de- 
veloped in  this  chapter,  that  there  is  con- 
stant change  going  on  in  all  parts  of  the 
body.  Particles  which  have  become  use- 
less are  taken  up  by  the  absorbents,  while 
the  formative  vessels  deposit  others  to  take 
their  places.  The  rapidity  with  which 
this  change  occurs,  depends  mostly  upon 
the  activity  of  the  individual.  The  busy 
laborer,  whether  the  labor  be  bodily  or  mental,  requires  more 
nourishment  than  the  indolent  man,  because  there  is  more 
waste  in  his  case,  from  the  wear  and  tear  occasioned  by  motion 
or  thought,  and  there  is  therefore  a  necessity  for  a  larger  sup- 
ply of  repairing  material.  The  difference,  it  is  true,  is  not  as 
great  in  regard  to  mental  labor,  as  in  regard  to  that  of  the 
body  ;  but  still  it  is  very  apparent.  This  dependence  of  the 
amount  of  change  in  the  system  upon  the  degree  of  activity  is 
very  manifest,  if  we  compare  different  animals  together  in  this 
respect.  I  have  already  contrasted  the  frog  and  the  canary 
bird  in  regard  to  respiration  (§  156,)  and  they  can  be  con- 
trasted in  this  respect  also.  As  the  frog  makes  but  little 
exertion  either  of  body  or  mind,  there  is  but  little  change  in  his 
body,  and  but  little  nutriment  is  required  to  supply  the  small 
waste  that  occurs.  But  in  the  ever  active  canary  there  is 
much  waste  from  this  action,  and  therefore  there  must  be  much 
eating  to  supply  the  material  of  repair.  As  he  sings  and  hops 
from  perch  to  perch,  his  mind  as  well  as  his  body  is  vastly 
more  active  than  that  of  the  frog ;  and  so  the  particles  in  his 
brain  and  nerves,  as  well  as  in  his  muscles,  are  oftener  changed. 
You  see  the  same  thing  still  more  strikingly,  if  you  contrast 
11 


122  HUMAN  PHYSIOLOGY. 


Change  varies  in  different  parts  of  the  body,  and  in  the  same  body  at  different  times. 

the  torpid  state  of  the  hibernating  animal  in  winter,  with  his 
active  state  in  the  warm  weather.  In  his  torpid  state  life  is 
dormant,  almost  at  a  stand  still,  sometimes  entirely  so.  And 
the  more  perfect  the  quiescence,  the  less  is  the  change,  and  the 
less,  therefore,  the  need  of  nutrition.  The  fat  which  he  lays 
up  in  the  autumn  (§  65)  answers  all  his  necessities  both  for 
nutrition  and  for  heat. 

183.  The  proportion,  thus  seen  to  exist  between  the  amount 
of  change  and  the  degree  of  activity,  is  exemplified  in  a  com- 
parison between  different  parts  of  the  body.     In  those  which 
are  most  actively  used  the  change  of  decay  and  repair  is  going 
on   most  constantly.     The  active   muscles  and  nerves  are  con- 
tinually changing  ;  while  the  bones,  which  are  only  passive  in- 
struments of  motion  are  changed  very  slowly.     And  it  is  a  sig- 
nificant fact,  that  in  the  case  of  the  muscles  and  nerves,  the 
waste  particles  are  to  a  large  extent  of  the  entirely  useless  kind 
(§    176),  for  they    are  mostly  absorbed  by   the  veins,  there 
being  in  them    but  few  lymphatics.     That  is,  whenever  we 
think,  or  feel,  or  move,  we  render  entirely  useless  quantities  of 
the  particles  which   make  up  the  structure  of  the  muscular  and 
nervous  systems,  and  these  are  got  rid  of  at  the  proper  out- 
lets, while  other  particles  immediately  take  their  places. 

184.  It  is  a  very  prevalent  notion  in  the  community,  that  the 
human  body  changes  throughout  once  in  every  seven  years. 
But  you  have  seen  that  the  change  is  very  unequal  in  different 
parts  of  the  body,  and  is  dependent  to  a  great  extent  on  cir- 
cumstances.     Sometimes    very    rapid   changes   occur.      Thus, 
when  one  has  been  much  reduced  by  sickness,  and  then  on  re- 
covery quickly  regains  his  usual  bulk,  the  body  is  very  exten- 
sively changed  in  a  short  period  of  time.     Ordinarily  the  cir- 
cumstance which  most  influences  the  change  is,  as  you  have 
seen,  the  degree  of  activity  which  exists,  whether  we  look  at 
an  animal  as  a  whole,  or  at  the  tissues  separately. 

185.  In  this  constant  change  going  on  in  the  body,  life  and 
death  may  be  said  to  be  brought  into  very  near  companionship. 
Every  act  of  the  mind,  and  every  movement  of  the  body  breaks 
down  some  of  the  structure ;  and  the  particles,  which  are  no 
longer  fitted  to  maintain  the  living  functions,  must  be  taken 
away  as  refuse  dead  matter,  and  new  particles  endowed  with 
vital   affinities   must   take   their   place.      Action,   destruction, 
repair,  are  the  successive  events  which  are  ever  occurring  in 
in  every  part  of  our  frame.     Action  is  followed  by  destruction, 
and  in   proportion  to  its  intensity ;  and  repair  is  necessary  to 


CELL-LIFE.  123 


The  formative  vessels  shown  by  the  microscope  to  be  cells. 

fit  for  further  action.  And  so  through  life  the  nutritive  func- 
tions are  thus  struggling  against  the  tendency  to  decay  and 
death,  till  at  length  at  the  appointed  limit  the  struggle  is  given 
over,  the  vital  affinities  release  their  hold,  the  common  laws  of 
dead  matter  take  possession  of  the  body,  and  the  soul  passes  to 
a  world  where  decay  and  change  are  unknown. 


CftAPTERIX, 

CELL-LIFE. 

186.  IN  previous  chapters,  in  treating  of  the  construction  of 
the  body,  I  have  spoken  of  the  formative  vessels  in  accordance 
with  the  common  language  of  physiologists.     The   common 
idea  has  been  hitherto,  that  the  work  of  construction  is  per- 
formed by  vessels  appended  to  the  capillaries.     The  capillaries 
were  considered  as  the  repositories  of  the  blood,  they  receiving 
it  from  the  arteries,  and  holding  it  in  readiness  for  the  use  to 
which  it  is  to  be  put  by  the  formative  vessels.     These  formative 
vessels,  it  was  supposed,  exercised  in  some  way  a  power  of  se- 
lection in  regard  to  the  constituents  of  the  blood,  and  also  a 
power  of  uniting  the  constituents  thus  chosen  into  particular 
forms.     In  this  way  physiologists   accounted  for  the  formation 
of  all  the  different  structures  in  the  bddy.     What  shape  these 
formative  vessels  had,  or  how  they  were  arranged  no  one  pre- 
tended to  know.     But  of  their  existence  no  one  had  a  doubt, 
for  there  seemed  to  be  an  absolute  necessity  for  supposing  some 
apparatus  of  vessels  appended  to  the  capillaries  for  the  per- 
formance of  this  function. 

187.  But  the  microscope  has  of  late  years  revealed  pheno- 
mena  which   have  changed   our   ideas   on   this  subject,  and 
which  must  to  some  extent  change  our  modes  of  expression  in 
relation  to  it  also.     It  has  showed  us   agencies  which  differ 
from  those  which  we  had  supposed  to  exist.     The  subject  is  an 
interesting  one,  and  I  propose  in  this  chapter  to  give  you  some 
glimpses  of  this  interior  life,  as  it  may  be  termed,  of  the  body. 

188.  It  is  found  by  the  aid  of  the  microscope,  that  all  the 
minute  operations  of  the  system  are  performed  by  the  agency 
of  cells.     They  are  not  such  cells  as  I  described  in  §  64  as 
existing  in  the  cellular  tissue,  which  are  mere  interstices,  com- 
municating together.     But  they  are  bladders  or  sacs,  and  ar« 


124 


HUMAK  PHYSIOLOGY. 


Cells  when  first  formed  globular.     Seen  in  the  blood  and  in  most  other  parts. 

filled  either  with  a  fluid  alone,  or  with  a  fluid  containing  some 
grains  of  solid  substance,  termed  molecules.  The  usual  form  of 
the  cell  when  it  first  appears  is  globular  or  spheroidal.  It  is 
seldom,  however,  seen  in  this  form  ;  for,  besides  the  change  of 
form  from  the  pressure  of  neighboring  cells,  the  cells  them- 
selves often  change  into  various  shapes,  as  you  will  see  in 
another  part  of  this  chapter. 

189.  Cells  can  be  seen  in  the  blood.  If  the  web  of  the  foot 
of  a  live  frog  be  placed  under  the  microscope,  you  can  see 
them  sweeping  along  in  the  blood  vessels,  like  so  many  little 
bladders,  varying  their  shape,  according  as  they  press  on  each 
other,  or  on  the  sides  of  the  vessel.  This  is  very  well  repre- 
sented in  Fig.  60,  in  which  a  portion  of  the  web  of  a  frog's  foot 
is  seen  as  magnified  110  diameters.  The  dark  irregular  spots 
which  you  see,  as  at  3,3,  are  pigment  cells,  which  give  the 
<»>lor  to  the  part. 

FIG.  60. 


CAPILLARIES  IN  THE  WEB  OF  A  FROG'S  FOOT. 

1 90.  Cells  may  be  seen  in  most  of  the  fluids  besides  the 
blood,  and  also  in  the  solids.     The  solid  parts  of  animal  bodies, 


CELL-LIFE. 


125 


Character  and  color  of  tissues  dependent  on  the  contents  of  cells. 

are  composed  either  of  cells,  or  of  structures  produced  by  cells, 
or  of  a  mixture  of  these  structures  with  cells.  The  same  can 
be  said  also  of  plants.  Cells,  therefore,  are  the  real  formative 
vessels  in  both  classes  of  organized  beings. 

191.  We  have  very  striking  exhibitions  of  the  FIG.  61. 
cells  in  the  lower  orders  of  animals.     The  Hydra, 

a  representation  of  which  is  given  in  Fig.  1, 
seems  to  be  made  up  of  little  else  than  cells. 
If  you  observe  under  the  microscope  one  of  its 
arms,  as  it  moves  about,  the  motion  appears  to 
be  a  motion  of  the  cells  upon  each  other. 
There  are  no  fibres  to  be  seen,  to  which  the  mo- 
tion can  be  attributed.  Fig.  61  represents  one  of 
these  arms  highly  magnified.  The  cells,  as  you 
see,  have  somewhat  of  a  spiral  arrangement. 

192.  The  character   of  many  of  the   tissues 
in  the   body  depends   on   the  contents  of  the 
cells.     The  cell  itself,  or  the  cell -wall,  as  it  is 
termed,  is  considered  to  be  always  the  same. 
But  the  contents  vary,  and  this  variation  makes 
generally  the  variation  in  the  character,  and  in 
the  color  also,  of  the  various  textures.     For  ex- 
ample, all  the  glands  are  constructed  essentially 
on  the  same  plan ;  and  their  difference  depends 
upon  the  contents  of  the  cells  in  them.     Thus 
the  liver  differs  from  the  tear-gland,  chiefly  be- 
cause the  former  has  cells  which  fill  themselves 
from  the  blood  with  the  components  of  bile,  while 

the  other  has  cells  which  fill  themselves  with  the  components 
of  the  tears.  The  color  of  various  parts,  as  the  iris  of  the  eye, 
the  skin  of  the  dark-colored,  the  hair,  &c.,  depends  upon  a 
coloring  matter,  which  constitutes  either  a  part  or  the  whole  of 
the  contents  of  particular  cells.  So  in  plants  the  various  colors 
displayed  result  from  the  various  coloring  matters  which  cer- 
tain cells  contain.  Some  contain  yellow  coloring  matter,  others 
red,  &c.  When  various  colors  appear  together  in  any  flower, 
there  are,  where  the  colors  bound  upon  each  other,  cells  lying 
side  by  side  which  contain  different  coloring  matters.  And  in 
the  shading  off  of  the  colors,  the  effect  is  produced  wholly  by 
the  variation  in  the  quantities  of  the  coloring  matter  in  the  cells. 

193.  It  is  clear  from  the  facts  which  have  been  stated,  that 
the  cells  have  a  selecting  power.     In  the  body  they  take  from 
the  common  pabulum  or  material,  the  blood,  such  constituents 


CELLS 


In  the  nrm  of  ths 
Hydra. 


126  HUMAN  PHYSIOLOGY. 

Cells  absorb  and  select.    Cells  real  laboratories. 

or  substances  as  they  need  for  their  particular  purposes.  I 
have  already  given  illustrations  of  this,  in  speaking  of  the 
difference  in  the  glands.  This  selecting  power  is  seen  in  the 
cells  everywhere.  Every  cell  contains  its  own  peculiar  consti- 
tuents, which  it  has  taken  from  the  blood.  For  example,  there 
are  fat-cells  which  receive  fatty  matter  from  the  blood,  rejecting 
every  thing  else ;  pigmentary  cells  receiving  nothing  but  color- 
ing matter  from  the  blood,  &c.  The  same  thing  appears  too 
in  plants.  There  are  cells  which  receive  from  the  sap  volatile 
oil ;  others,  fixed  oil ;  others,  starch ;  others,  coloring  matter, 
&c. 

194.  Fluids,  and  sometimes  gases  enter  the  cells  continually. 
The   pores   through  which   they  enter   are   not   visible   even 
through  the  microscope,  but  of  course  such  pores  must  exist. 
Their  entrance  is  controlled  by  the  selecting  power  to  which  I 
have  alluded. 

195.  This  selecting  absorption  thus  performed  by  cells,  as 
revealed  by  the  microscope,  is  one  of  the  most  wonderful  and 
mysterious  phenomena  in  the  material   world.     There  is  here 
a  power  in  these  cells  which  is  unaccountable.     The  selection 
is  made  by  the  little  cell  as  unerringly,  as  if  its  pores  were  con- 
trolled by  an  intelligence  residing  there.     It  has  been  said  that 
this  selection  is  a  mere  result  of  affinity ;  that  a  certain  affinity 
exists  between  the  contents  of  the  cell,  or  the  cell  itself,  for  the 
constituents  which  are  absorbed.     But  if  it  be  so,  the  mystery 
comes  no  nearer  to  being  solved  than  before.     For  how  are 
these  affinities,  so  numerous  and  various,  established,  and  what 
are  the  principles  by  which  they  are  governed  ?     In  either 
case  the  wisdom  and  power  of  the  Creator  may  be  considered 
as  making,  in  this  minute  interior  life  of  all  organized  sub- 
stances, some  of  their  most  wonderful  manifestations. 

196.  There  is  not  only  a  selecting  power  in  the  cell,  but  there 
is  often  a   converting  power,   by  which  new  compounds  are 
formed  from  the  constituents  introduced  into  it.     The  cell  in 
this  case,  though  so  small  as  to  be  seen  only  by  a  microscope 
of  considerable  power,  is  a  real  laboratory,  effecting  chemical 
changes  in  its  contents.     There  can  often  be  seen  quite  a  brisk 
movement  in  the  molecules  in  the  cell  while  these  changes  are 
going  on. 

197.  Some  cells  produce  other  cells.     This  is  the  sole  office 
of  some  of  them.     In  some  cases  new  cells  are  made  by  a 
separation  of  a  cell  into  two  or  more.     A  sort  of  hourglass 
contraction  takes  place  at  the  middle,  by  an  inflection  or  fold- 


CELL-LIFE.  127 


Different  offices  of  cells.    Office  of  red  cells  in  the  blood. 

ing  in  of  the  inner  cell-wall,  for  the  cell  has  two  walls.  At  the 
tame  time  the  cell  becomes  elongated.  An  entire  separation 
into  two  cells  is  thus,  after  a  little  time,  effected ;  and  then  each 
of  these  cells  becomes  two  more,  and  so  on.  In  other  cases 
cells  are  formed  within  cells.  When  this  takes  place,  the 
nucleus,  that  is  an  aggregation  or  mass*  of  solid  matter  in  the 
cell,  separates  into  two  different  parts,  each  of  which  has  a  cell 
formed  around  it. 

198.  Cells,  as  you  have  already  seen,  do  not  all  perform  the 
same  office,  but  there  are  cells  for  a  great  variety  of  purposes. 
A  consideration  of  these  will  develope  to  you  still  greater  won- 
ders in  the  cell-life,  and  show  you  in  the  most  interesting  man- 
ner how  great  the  Creator  is  in  the  minute  operations  of  nature, 
as  well  as  in  those  which  are  large  and  obvious  to  the  naked 
eye. 

199.  There  are  different  kinds  of  cells  in  the  blood.     There 
are  colored  and  colorless  ones.     The  office  of  the  colorless  ones 
has  not  yet  been  satisfactorily  determined.     But  we  know  more 
about  the  colored  ones.     These  give  the  red  color  to  the  blood. 
They  are  not  red  when  looked  at  singly,  but  are  of  a  yellow 
cast ;  and  the  red  color  appears  only  when  several  are  together. 
One  office  of  these  colored  cells  is  to  carry  oxygen  to  all  parts 
of  the  system,  and  return  the  carbonic  acid  to  the  lungs  to  be 
thrown  off.     By  carrying  these  cargoes  back  and  forth  in  the 
circulation,  these  little  cells  perform  a  very  important  office. 
A  very  valuable  part  of  the  cargo  of  these  cells  is  iron.     In  low 
states  of  the  system,  when  the  red  cells  are  deficient,  the  ad- 
ministration of  iron  in  some  form  is  often  found  to  be  very 
effectual,  in  connection  with  a  good  diet,  in  remedying  the  defi- 
ciency.    The   proportion    of  these   red   cells  varies   much   in 
different  animals.     It  is  largest  in  those  which  are  the  most 
active,  and  which,  therefore,  as  you  saw  in  the  chapter  on 
Respiration,    consume   the   largest  quantity  of  oxygen.     The 
proportion  is  greater  generally  in  birds  than  in  the  mammalia, 
and  it  is  much  greater  in  the  latter  than  in  reptiles  or  fishes. 
In  man  it  varies  much  in  different  individuals.     These  cells 
are  abundant  in  the  ruddy,  strong,  and  active ;  while  it  is  other- 
wise in  the  inactive,  pale,  and  feeble. 

200.  There  are  cells  for  absorption,  and  cells  for  secretion 

*  To  the  common  ear  the  word  mass,  which  is  ordinarily  used  in  relation  to  aggregates 
of  some  size,  sec:ns  out  of  place  when  applied  to  a  collection  of  molecules  which  is  so 
small,  that  it  c  ..  only  be  seen  by  a  microscope  of  high  power  ;  but  though  fco  small,  it  is 
to  the  little  • .  jntaining  it  a  mass. 


128  HUMAN   PHYSIOLOGY. 

Manner  in  which  absorption  is  performed  by  cells. 

and  excretion.  Of  these  I  will  give  some  examples.  I  have 
said  in  the  chapter  on  Digestion,  that  the  vessels  called  lacteala 
absorb  chyle  from  the  contents  of  the  intestine.  It  was  formerly 
supposed  that  they  did  this  through  their  open  mouths  on  the 
surface  of  the  mucous  membrane.  But  the  microscope  has 
shown  that  this  is  not  so.  The  absorption  is  accomplished  by 
cells,  which  are  developed  for  this  purpose  at  the  extremities 
of  the  lacteals.  They  take  up  the  chyle  and  discharge  it  into 
the  lacteals,  and  they  are  dissolved  away  in  the  very  act  of 
emptying  themselves.  A  new  crop  therefore  of  cells  appears 
eve  Y  time  the  process  of  absorption  is  to  be  performed.  And, 
wha:  is  still  more  curious,  every  time  that  absorption  is  to  take 
place,  ihere  is  cast  off,  as  a  preparatory  step,  a  sort  of  pavement 
of  cells  from  over  every  point  in  the  mucous  membrane  where 
there  is  n  extremity  of  a  lacteal.  The  absorbing  cells  are 
thus  uncovered,  so  that  they  can  perform  their  duty.  All  this 
can  be  made  clear  by  the  following  diagram.  I  must  premise 
that  the  surfac  of  the  mucous  membrane  of  the  intestine  is  not 
a  perfectly  smo(  h  surface,  but  examined  by  a  microscope  it  is 
seen  to  be  covered  with  eminences  and  depressions.  Absorp- 
tion takes  place  on  the  eminences,  while  the  depressions  are 
the  seats  of  secretion.  In  the  diagram.  Fig.  62,  you  have  a 

FIG.  62. 


DIAGRAM  SHOWING  ABSORPTION  IN  A  MUCOUS  MEMBRANE. 

representation  of  the  arrangement  of  one  of  the  eminences 
highly  magnified.  A,  represents  it  as  it  is  in  the  intervals 
of  digestion  when  absorption  is  not  going  on,  and  B  as  i-t  is 
during  absorption  ;  a  a  are  the  absorbent  vessels  or  lacteals  ; 
b  b  basement  membrane,  as  it  is  termed,  an  exceedingly  thin 
membrane  acting  as  a  basement  to  the  pavement  cells  c  c  ;  d  d, 


CELL-LIFE.  129 


Manner  in  which  secretion  is  effected  by  them. 


the  absorbing  cells.  When  absorption  is  not  going  on,  the 
prominence  is  somewhat  shrunken,  and  the  pavement  cells 
cover  it.  There  are  some  granules  or  small  grains,  c?,  in  A, 
which  are,  it  is  supposed,  the  germs  of  the  absorbing  cells, 
which  you  see  developed  in  B.  When  absorption  is  taking 
place,  the  prominence  is  swelled  out  as  represented,  the  lacteal 
vessels  are  full,  and  the  absorbing  cells  appear  at  their  ex- 
tremities, while  the  pavement  cells  have  been  thrown  off,  so 
that  the  chyle  may  have  free  access  to  the  absorbing  cells 
through  the  pores  or  interstices  of  the  basement  membrane. 

201.  While   absorption   thus   goes   on    in    the   eminences, 
secretion  takes  place  in  the  depressions.     The  diagram,  Fig.  63, 

FIG.  63. 


DIAGRAM  SHOWING  SECRETION  IN  A  MUCOUS  MEMBRANE. 

represents  one  of  these  depressions,  or  follicles,  as  they  are 
termed,  in  two  opposite  states,  when  secreting,  and  when  not 
secreting.  In  A,  secretion  is  not  going  on,  and  the  cells  e,  in 
the  follicle  remain  quiet.  In  B,  on  the  other  hand,  secretion 
is  taking  place,  and  it  is  done  by  the  casting  off  of  cells,  as 
represented.  These  cells  discharge  their  fluid  contents  into 
the  cavity  of  the  intestine,  and  disappear,  while  other  cells  take 
their  places.  These  follicles  are  really  little  glands.  And  the 
various  glands,  the  salivary  glands,  the  liver,  the  pancreas,  &c., 
are  made  up  essentially  of  such  follicles  arranged  in  different 
ways.  You  see,  therefore,  in  this  diagram,  the  manner  in 
which  secretion  is  effected  everywhere.  The  secreted  matter 
is  received  by  the  absorbing  cells,  through  the  interstices  of  the 
basement  membrane,  from  the  blood  in  the  capillaries  which  lie 
under  this  membrane. 

202.  The  pavement  cells,  of  which  I  have  spoken,  cover 
every  part  of  the  mucous  coat  or  membrane,  and  answer  as  a 
protection  to  it.  There  is  a  similar  arrangement  over  the 
whole  outer  surface  of  the  body.  Next  to  the  true  skin  is  a 


130 


HUMAN  PHYSIOLOGY. 


Muscles  made  up  of  cells.    Their  tontraction  nnd  relaxation. 

basement  membrane,  and  upon  these,  as  in  the  case  of  the 
mucous  coat  of  the  alimentary  canal,  lie  pavement  cells.  These 
cells,  constituting  the  cuticle  or  scarf-skin,  are  much  more 
numerous  than  in  the  alimentary  canal.  There  are  many 
layers  of  them.  The  outer  cells  dry  by  exposure  to  the  air, 
and  become  scales.  As  these  are  rubbed  off.  the  cells  below 
take  their  places  ;  and  there  is  a  constant  supply  of  fresh  cells 
from  the  basement  membrane. 

203.  There  are  some  cells  which  are  devoted  entirely  to  the 
production  of  motion,  for  an  ordinary  muscle  is  composed  of 
great  numbers  of  chains  of  cells  included  in  sheaths  bound  to- 
gether. A  muscle  appears  to  the  naked  eye  to  be  made  up  of 
fibres.  Each  one  of  these  fibres  is  found  by  the  miscroscope  to 
be  composed  of  from  500  to  800  fibrillce,  or  minute  fibres. 
And  each  of  these  fibrillse  is  a  series  or  chain  of  cells.  In  Fig. 
64,  a,  is  represented  a  fibre  as  seen  under  the  microscope, 

FIG.  64. 


a 


FIG.  65. 


FIBRE  OF  A  MUSCLE. 

showing  the  fibrillse  of  which  it  is  com- 
posed. They  are  separated  at  the  broken 
end  by  the  violence  in  tearing  the  fibre. 
In  6,  you  see  one  of  the  fibrillae  very  highly 
magnified,  showing  that  it  is  a  chain  of 
cells.  In  the  diagram,  Fig.  65,  is  repre- 
sented the  condition  of  a  fibrilla  in  the 
two  states  of  contraction  and  relaxation. 
In  a  it  is  relaxed.  In  6  it  is  contracted, 
the  cells  being  shortened,  and  at  the  same 
time  widened.  And  as  all  the  cells  in  the 
muscle  are  thus  widened  when  the  muscle 
contracts,  we  see  the  cause  of  the  well 
known  swelling  out  of  muscles  when  they 
are  in  action.  That  you  may  form  some 
idea  of  the  size  of  these  cells  in  muscles,  I 
will  state  that  in  the  space  of  the  square 
of  a  tenth  part  of  an  inch,  thus,  there 

are  over  100,000  of  these  cells.  M   When 


MUSCULAR  FIBRIL; 

a  relaxed  ;  6  contracted. 


CELL-LIFE. 


131 


Hoofs,  horns,  nails,  and  teeth  made  by  cells. 


a  large  muscle  contracts  what  an  innumerable  multitude  of 
these  cells  are  set  in  action  ! 

204.  There  are  cells  whose  office  it  is  to  make  certain  solid 
deposits.  Hoofs,  horns,  nails,  and  teeth  are  made  in  this  way. 
Even  the  hard  enamel  of  the  teeth  is  constructed  by  cells. 
They  deposit  it  in  the  form  of  prisms  of  hexagonal  shape  as 
seen  in  Fig.  66,  which  represents  a  vertical  section  of  enamel 
as  seen  under  the  microscope.  Their  shape  is  more  plainly  seen 
in  A,  Fig.  67,  which  represents  a  transverse  section  of  enamel. 
The  line  of  these  prisms  is  generally  wavy,  but  they  are  for  the 
most  part  parallel  to  each  other.  At  B  are  some  of  these  prisms 
separated.  They  are  more  magnified  here  than  in  Fig.  66. 


FIG.  66. 


VERTICAL  SECTION  OF  ENAMEL. 
FIG.  67. 


ENAMEL. 
A,  Transverse  section.    B,  Separated  prisms  of  it 

205.  Perhaps  the  most  wonderful  exhibitions  of  the  functions 
of  the  cell  are  presented  to  us  in  the  nervous  system.  The 
nerves  are  bundles  of  tubes  of  exceeding  fineness.  They  vary 
from  TsVoth  to  i  o.oouth  of  an  inch  in  diameter.  Now,  each 
of  these  little  tubes,  or  tubuli,  as  they  are  called,  was  once  a 
chain  of  cells.  The  cells  in  each  chain  or  row,  as  the  micros- 


132  HUMAN  PHYSIOLOGY. 

Nerves  composed  of  tubes  made  from  cells.     Cells  in  the  gray  substance  of  the  brain. 

cope  has  shown,  gradually  became  incorporated  together  to  be- 
come a  tube,  and  in  this  tube  is  contained  the  true  nervous 
matter.  And  it  is  supposed  that  each  of  these  tubuli  preserves 
itself  separate  and  distinct,  from  its  origin  in  the  brain,  or  some 
other  of  the  central  organs  of  the  nervous  system,  to  its  ter- 
mination in  some  fibre,  or  on  some  surface.  For  no  communi- 
cations between  the  tubuli  have  ever  been  foun,d  by  any  micros- 
copist.  The  manner  in  which  these  tubuli  are  made  from  cells 
may  be  illustrated  by  the  diagram 
in  Fig.  68,  in  which  the  steps  by  FIG.  68. 

which  the  row  of  cells  A  becomes         A  B 

the  tube  B  are  represented. 

206.  It   is    these   tubuli,   thus 
formed  from  cells,  that  constitute 
the  means  of  nervous  communica- 
tion between  all  parts  of  the  sys- 
tem.    Thus,  when  a  muscle  con- 
tracts in  obedience   to    the   will, 

an  impression  is  conveyed  through  those  tubuli  that  connect  the 
brain  with  the  fibres  of  the  muscle,  or  rather  with  the  cells  of 
which  these  fibres  are  composed.  These  tubuli  exist  in  all  the 
nerves,  and  in  the  white  parts  of  the  brain  and  spinal  marrow. 
They  transmit,  but  they  have  nothing  to  do  with  originating 
what  is  transmitted.  This  is  done  by  another  part  of  the  nervous 
system,  the  reddish  gray  substance,  which  is  seen  in  the  brain 
and  spinal  marrow,  as  entirely  distinct  from  the  white  portion. 
This  gray  substance,  in  which  all  nerve  force,  as  it  is  termed,  is 
produced,  is  made  up  chiefly  of  cells.  These  cells,  which  have 
a  nucleus  or  central  particle,  are  originally  globular,  but  many 
of  them  assume  various  shapes,  and  often  shoot  out  branches. 
Some  of  the  shapes  are  very  fantastic  as  represented  in  Fig.  69. 
These  are  magnified  200  diameters. 

207.  In  the  views  which  I  have  given  of  cell-life,  I  have  not 
attempted  to  describe  all  the  phenomena  which  have  been  dis- 
covered, but  only  enough  of  them  to  give  the  student  a  general 
view  of  this  interior  unseen  life,  that  is  at  work  so  busily  at 
every  point  of  every  living  substance.     The  cell,  you  have  seen, 
performs  a  great  variety  of  functions.     It  is  the  agent  by  which 
all  vital  operations  are  carried  on.     The  very  beginning  of  life, 
so  far  as  we  can  see,  is  in  the  cell  which  the  microscope  reveals 
to  us.     Its  first  manifestation  is  here.     We  can  suppose  a  germ 
as  the  origin  of  a  cell,  but  we  do  not  see  it  if  it  exist. 

208.  All  animated  nature  is  built  up  by  cells.     The  first 


CELL-LIFE. 


133 


All  organized  substances  built  up  by  cells. 


FIG.  69. 


NERVE  CELLS  IN  THE  GRAY  SUBSTANCE. 

thing  which  comes  from  the  supposed  germ  is  a  cell.  And 
this  single  cell  is  the  parent  of  all  the  cells  which  build  up  the 
whole  structure,  whatever  it  be.  It  is  by  these  cells  thus  pro- 
duced, that  all  plants  and  animals  are  constructed.  "A  globu- 
lar mass,"  says  Carpenter,  "  containing  a  large  number  of  cells 
is  formed  before  any  diversity  of  parts  shows  itself;  and  it  is 
by  the  subsequent  development,  from  this  mass,  of  different 
sets  of  cells,  of  which  some  are  changed  into  cartilage,  others 
into  nerve,  others  into  muscle,  others  into  vessels,  and  so  on, 
that  the  several  parts  of  the  body  are  ultimately  formed.  Of 
the  cause  of  these  transformations,  and  of  the  regularity  with 
which  they  take  place  in  the  different  parts,  according  to  the 
type  or  plan  upon  which  the  animal  is  constructed,  we  are  en- 
tirely in  the  dark ;  and  we  may  probably  never  know  much 
more  than  we  do  at  present." 

209.  A  beautiful  exemplification  of  what  has  just  been  stated 
is  seen  in  the  development  of  the  animal  in  the  interior  of  an 
egg,  and,  particularly-  in  the  egg  of  the  bird  tribe.  By  an  ex 

12 


134  HUMAN  PHYSIOLOGY. 

Arrangement  of  the  parts  of  the  egg. 

animation  of  different  eggs  at  different  stages  of  the  process  of 
hatching,  the  various  steps  in  the  development  of  the  animal 
have  been  observed  and  noted.  It  is  a  series  of  most  wonderful 
processes,  that  go  on  concealed  from  our  view  by  that  sym- 
metrical inclosure  of  lime.  Of  these  I  will  present  the  general 
outlines.  In  the  middle  of  the  egg  is  the  yellow  yolk,  com- 
posed of  albumen  and  oil  globules.  It  is  surrounded  by  an  ex- 
ceedingly thin  sac,  which  keeps  it  separate  from  the  albumen, 
the  white  of  the  egg  that  envelopes  it.  The  yolk,  6,  Fig.  70,  is 


SECTION  OF  A  BIRDS'  EGG. 

lighter  than  the  white,  and  it  therefore  always  seeks  the  highest 
point  in  the  egg.  But  there  is  a  particular  contrivance  which 
prevents  it  from  actually  touching  the  shell.  It  is  held  down 
by  two  very  delicate  ligaments  e,e,  connecting  it  with  the  white 
lining  of  the  shell.  And  you  will  observe,  too,  that  the  cica- 
tricula,  or  germ-spot,  a,  which  is  a  collection  of  cells  beginning 
the  process  which  is  to  form  the  animal,  being  lighter  than  the 
yolk  is  always  at  the  top  of  it,  in  order  to  receive  the  warmth 
from  the  body  of  the  bird  as  it  sets  upon  its  eggs.  Besides  all 
this,  there  is  at  the  blunt  end  of  the  egg,  /,  a  bubble  of  air 
which  is  intended  as  an  invigorating  draught  for  the  lungs 
of  the  young  bird,  preparatory  to  its  bursting  its  shell. 

210.  When  the  processes  preparatory  to  the  formation  of  the 
animal  commence,  the  yolk  itself  is  composed  in  part  of  cells, 
as  represented  in  Fig.  71,  A.  In  the  midst  of  it  there  is  a 
germinal  spot,  a,  with  a  vesicle  in  it,  b.  This  vesicle  produces 


CELL-LIFE. 


135 


Succession  of  cells  in  the  yolk  before  the  animal  is  formed. 


FIG.  71. 


B       ? 


DEVELOPMENT  OF  CELLS  IN  THE  YOLK  DURING  INCUBATION. 

a  cluster  of  cells.  But  these  cells,  and  those  which  in  part 
compose  the  yolk  are  temporary,  and  all  disappear.  Before, 
however,  the  cluster  of  cells  in  the  germinal  spot  disappear, 
there  are  seen  in  the  midst  of  them  two  twin  cells.  These 
multiply  ;  and  what  is  singular,  they  do  it  by  doubling,  so  that 
there  are  successively  4,  8,  16,  32,  &c.  At  length  there  is  a 
mass  of  them,  like  a  mulberry,  as  at  e,  in  B.  This  mass  then 
sends  off  cells  at  its  edges  which  makes  a  layer,/,  all  round 
the  yolk  as  represented  in  C.  A  second  layer,  ^,  is  formed 
inside  of  the  first  as  seen  in  D.  In  the  case  of  the  higher 
animals  a  third  layer  is  added. 

211.  There  is  no  formation  of  the  animal  yet.  But  now  a 
single  large  cell  appears  in  the  centre  of  the  mulberry-shaped 
mass  of  cells,  and  from  this  begins  the  formation  of  the  animal. 
All  the  other  parts  of  the  egg — the  cells,  the  yolk,  the  white — 
are  tributary  to  the  action  which  proceeds  from  this  cell. 
Within  its  wall  is  a  ring-like  nucleus.  This  takes  the  shape  of 
a  pear,  and  then  it  is  afterward  very  much  like  a  violin. 
From  this  nucleus  are  produced  cells  which  form  all  the 
various  parts  of  the  animal,  the  heart,  lungs,  stomach,  brain, 
limbs,  <fec.  And  these  are  made  out  of  the  yolk  and  the  white 
of  the  egg. 


136  HUMAN"  PHYSIOLOGY. 

Office  of  the  allantois.     All  animals  and  plants  come  from  simple  cells. 

212.  There  is  one  contrivance  made  use  of  during  this  de- 
velopment of  the  animal,  which  must  not  pass  unnoticed.     A 
very  delicate  bag,  called  the  allantois,  is  formed,  which  is  attach- 
ed to  the  embryo,  and  at  length  almost  envelopes  it.     The  office 
of  this  is  to  expose  the  blood  of  the  embryo  to  the  air.     This  is 
accomplished  through  the  pores  of  the  shell,  against  which  the 
allantois  with  its  minute  blood-vessels  presses.     This  organ  is 
in  fact  the  temporary  breathing  apparatus  of  the  developing 
animal.     The  development  can  be  arrested  by  smearing  over 
the  egg  with  some  substance  that  will  prevent  the  entrance  of 
air  through  the  shell.     When  the  animal  is  fully  developed, 
and  is  ready  to  come  forth  from  his  prison,  he  inhales  the  air 
provided  for  him,  as  before  described,  and  with  the  strength 
given  to  him  by  the  stimulus  of  the  air  in  his  lungs,  he  bursts 
the  crust  of  lime  that  incloses  him. 

213.  I  have  described  these  processes  which  take  place  in 
the  egg,  in  order  that  you  may  see  the  mysterious  connection 
between  the  simple  cells  that  form  in  the  beginning,  and  the 
full  development  of  the  complete  and  diversified  organization. 
In  the  formation  of  all  animals,  and  we  may  say  plants  also, 
there  is  a  similar  connection,  varied  of  course  according  to  the 
circumstances  of  each  case.     As  we  observe  the  various  steps 
of  the  process,  the  mind  is  filled  with  wonder.     As  we  look  at 
the  egg,  containing  nothing  but  a  yolk  surrounded  by  albumen, 
with  its  little  cell  of  air  at  the  end,  and  see  it  wholly  separated 
from  every  living  organization,  shut  up  entirely  by  itself  in  a 
wall  of  lime,  we  can  hardly  believe  that  the  mere  application 
of  heat  will  cause  in  the  contents  a  series  of  processes,  which 
will  result  in  an  animal  so  complete,  that  it  can  burst  its  own 
prison  walls,  and,  as  is  the  case  with  some  of  the  tribe,  at  once 
walk  forth  into  the  open  air.     The  processes  by  which  all  this 
is  effected  have  been  narrowly  watched  by  the  eager  eye  of 
scientific  inquiry ;  but  the  mystery  remains  unsolved,  and  pro- 
bably to  man  it  will  always  remain  so. 

214.  From  the  views  which  I  have  presented  in  this  chapter 
it  is  manifest,  that  the  grand  distinction  between  organized  and 
unorganized  substances  is  to  be  found  in  this  cell-life  of  the 
organized.     In  unorganized  substances  particles  or  molecules 
are  the  only  things  which  we  know  of  as  being  concerned  in 
their  formation.     But  in    the  construction    of  organized  sub- 
stances or  beings,  every  thing  is  done  by  the  agency  of  cells. 
And  in  this  cell  -life  of  the  living  world  we  have  another  beauti- 
ful example  of  the  divers  and  almost  numberless  results,  which 


CELL-LIFE.  137 


The  power  of  the  Deity  shown  in  the  minute  operations  of  Nature. 

the  Creator  works  out  by  simple  and  single  means.  As  gravi- 
tation holds  atoms  together  in  masses  of  every  size  from  the 
minutest  to  the  largest,  and  keeps  the  mighty  orbs  in  their 
appointed  circuits,  so  the  cell-organization  constructs  and  moves 
all  living  things,  however  small,  however  large,  and  however 
diversified. 

215.  As  we  examine  the  various  workings  of  this  cell-life,  wa 
can  not  but  perceive  the  truth  of  the  old  adage,  Natura  in 
minimis  maxima  est — nature  is  greatest  in  its  smallest  things. 
The  power  of  mere  bulk  or  mere  force  we  can  comprehend  by 
mental  addition,  however  great  that  power  may  be.     We  can 
imagine  a  power  which  we  see,  to  be  indefinitely  multiplied, 
and  thus  can  form  the  idea  of  immense  power.     But  when 
with  the  microscope  we  see  minute  cells   working  out  such 
results  as  we  have  contemplated  in  this   chapter,  and  inquire 
how  it  is  done,  we  see  that  there  is  a  hidden  power  here  that 
utterly  defies  our  conception.     The  mechanics  and  the  chemis- 
try of  the  cell,  who  can  understand  them  ?     From  the  inscruta- 
ble movements  of  this  hidden  power,   at  work  wherever  life  is, 
in  the  cells,  its  laboratories,  we  get  a  higher  idea  of  Omnipo- 
tence than  we  can  get  from  the  grandest  and  most  terrific  ex- 
hibitions of  mere  force.     We  get  from  them  the  idea  of  an  all- 
pervading,  as  well  as  an  all-wise  power,  working  not  merely  in 
every  locality,  but  at  every  point  of  the   universe.     And  the 
revelations  which  the  microscope  makes  to  us  seem  to  draw  us 
very  near  to  the  Infinite.     As  we  gaze  with  wonder  and  delight 
at  the  secret  operations  of  his  power  thus  opened  to  us,  we  seem 
almost  to  be  admitted  to  his  presence ;  and  even  our  awakened 
curiosity,  amid  the  wonders  now  brought  into  our  field  of  vision, 
does  not  suffice  to  remove  the  awe  which  almost  oppresses  us. 

216.  How  great  is    the  inner  beauty  of  the  living  world 
around  us !     We  admire  the  symmetrical  forms,  and  the  beau- 
tiful colors  which  nature  presents  to  us  in  such  variety ;  but 
there  is  an  inner  world  of  beauties  throughout  nature,  still  more 
perfect  and  resplendent,  which  is  hidden  from  the  naked  eye 
of  man,  though  it  is  all  open  to  the  Omniscient.     If  you  would 
get  some  idea  of  the  beauty  of  this  inner  world,  take  the  most 
delicately  beautiful  of  all  the  specimens  of  man's  workmanship, 
and  examine  it  with  a  microscope  ;  and  then  compare  it  with 
some  living  texture  or  coloring.     Compare  in  this  way,   for 
example,  the  most  perfect  painting  of  a  flower  with  the  flower 
itself.     The  painting  loses  all  its  beauty  as  it  is  magnified ;  but 
in  the  bosom  of  the  flower  the  microscope  developes  to  you 

12* 


138  HUMAN   PHYSIOLOGY. 

The  inner  beauty  developed  by  the  microscope. 

beauties  far  transcending  those  which  are  seen  by  the  unassisted 
eye.  Even  such  living  structures  as  are  unattractive  to  the 
naked  eye,  present  under  the  microscope  wonderful  beauty  in 
the  delicate  lines  of  their  textures.  It  is  true  of  every  one  who 
has  used  this  instrument  in  his  observation  of  nature,  that  he  is 
impressed  with  the  fact,  that  great  as  is  the  beauty  of  nature, 
as  we  look  out  upon  it,  it  is  vastly  inferior  both  in  kind  and  in 
amount  to  that  inner  beauty  seen  so  completely  by  the  all- 
seeing  Eye,  and  now  developed  to  us  in  part  by  the  skill  and 
ingenuity  of  man.  And  it  suggests  to  us  the  hope,  that  in  a 
new  state  of  being,  and  with  higher  faculties,  we  shall  be  able 
to  look  farther  into  these  inner  beauties  of  the  universe,  than 
we  now  can  with  all  the  aids  which  our  ingenuity  can  devise. 


PART  THIRD, 


CONTAINING 


CHAPTER  X.-Tmc  NERVOUS  SYSTEM.  CHAPTER  XL-Tint  Boras.  CHAPTER  Xri.-Tmi 
MUSCLES.  CHAPTER  XIII.-THE  LANGUAGE  OP  THE  MUSCLES.  CHAPTER  XIV.- -Tin 
VOICE.  CHAPTER  XV.-THE  EAR.  CHAPTER  XVI.-THE  EYE.  CHAPTER  XVII.-THB 
CONNECTION  OF  THE  MIND  WITH  THE  BODY.  CHAPTER  XVIII. — DIFFERENCES  BETWEEN 
MAN  AND  THE  INFERIOR  ANIMALS.  CHAPTER  XIX.-VARIKTISS  OF  THK  HUMAN  RACK. 
CHAPTER  XX.-LiFK  AND  DKATH. 


CHAPTER  X. 

THE  NERVOUS  SYSTEM. 

217.  THUS  far  we  have  contemplated  man  merely  as  a  struc- 
ture.    We  have  observed  the  means    by  which  the  body  is 
built  and  is  kept  in  repair.     We  have  seen  that  in  regard  to 
these  functions  of  nutrition,  man  and  all  animals  have  much  in 
common  with  plants.     So  far  as  these  functions  are  concerned, 
they  vary  from  plants  only  in  the  modes  by  which  the  nutrition 
is  effected.     The  difference  in  this  respect  is  not  an  essential 
one.     The  absorbents  in  the  root  of  the  plant  do  for  the  plant 
what  the  lacteals  in  the  digestive  organs  do  for  the  animal, 
the    difference   between   them   being   only    according   to   the 
differing  circumstances.     So  also,  circulation  and  formation  are 
in  all  essential  points  the  same  in  these  two  different  depart- 
ments of  animated  nature.     The  microscope  has  in  the  most 
striking  manner  shown  this  to  be  true  of  formation,  for  vegeta- 
bles and  animals  are  alike  constructed,  as  you  have  seen,  by 
cells. 

218.  The  functions  of  which  I  have  treated  in  the  previous 
chapters,  as  being  common  to  plants  and  animals,  are  called  the 
functions  of  organic  life,  because  they  concern  merely  the  struc- 
ture, the  organization.     But  there  are  other  functions.     The 
body,  with  all  its  complicated  parts,  is  constructed  and  kept  in 
repair  for  certain  uses.     These  uses  are  secured  by  the  nervous 
system, — a  system,  which  I  have  spoken  of  in  §  32,  as  being 
superadded  to  what  the  animal  has  in  common  with  the  plant, 
and  which,  therefore,  constitutes  the  essential  difference  between 
the  animal  and  the  plant.     This  system  furnishes  the  means 
of  the  relations  of  the  animal  to  the  world  around  him.     He 
receives   his   impressions  from   external   things    through   this 


140  HUMAN  PHYSIOLOGY. 

The  nervous  system  and  its  subordinate  instruments. 

system  ;  and  through  it  he  acts  upon  external  things.  He 
feels  through  the  nerves,  and  by  the  nerves  excites  those 
motions  by  which  he  acts  on  both  material  and  immaterial 
existences.  The  functions,  therefore,  which  are  performed 
through  this  system,  are  called  functions  of  animal  life,  in  dis- 
tinction from  the  functions  of  organic  life,  which  are  common 
to  vegetables  and  animals.  They  are  sometimes  also  called 
functions  of  relation,  in  view  of  the  relations  which  it  estab- 
lishes between  sentient  and  moving  beings,  and  all  external 
things. 

219.  But  there  are  intermediate  instruments,  through  which 
the  nervous  system  exercises  its  functions.     The  nerves  do  not 
themselves  move,  but  they  excite  motion  in  muscles,  and  these 
move  bones  and  other  parts.     Neither  is  sensation  performed 
by  the  nerves   alone.     The  different  senses,  for  example,  have 
different  organs,  with  arrangements  differing  according  to  the 
kind  of  sensation.     Mere  nerves  do  not  alone  see,  or  hear,  or 
taste,  or  smell,  or  touch.     There  are  special  organs  constructed 
for  these  purposes  ;  and  through  these  the  nerves  receive  im- 
pressions.    Thus  the  nerve  of  sight  cannot  of  itself  see ;  but 
the  eye  being  there,  so  formed  as  to  have  pictured  on  a  mem- 
brane the  images  of  objects,  the  nerve  receives  an  impression 
from  these  images,  and  this  impression  is  transmitted  through 
the  trunk  of  the  nerve  to  the  brain,  where  the  mind  takes  cog- 
nizance of  it ;  and  this  constitutes  seeing. 

220.  While  then  the  nervous  system  is  the  great  essential 
means  of  connection  between  the  mind  and  external  things, 
there  are  other  subordinate  means,  as  we  may  consider  them. 
They  are  organs  of  various  kinds,  through  which  the  nerves  act 
and  are  acted  upon.     The  nervous  system,  therefore,  may  be 
viewed  as  presiding  over  the  sentient  and  moving  machinery,  in 
the  complex  structure  of  the  human  system,  which  we  have 
been  examining  in  the  previous  chapters. 

221.  The  nervous  system  in  the  lower  orders  of  animals  is 
very  simple,  and  forms  an  exceedingly  small  part  of  the  animal. 
But,  as  we  rise  in  the  scale,  we  find  that,  as  the  limits  of  rela- 
tion  to   external  things  enlarge,    this   system  becomes  more 
prominent ;  till,  in  man,  in  whom  these  relations,  both  mental 
and   physical,   are  much   more  extensive   than   in  any  other 
animal,  it  is  very  prominent  and  greatly  complicated. 

222.  The  interest  of  the  class  of  subjects,  now  to  be  opened 
to  you,  much  transcends  that  of  the  subjects  which  we  have 
already  gone  over.     If  you  look  at  a  child  as  it  first  opens  its 


THE  NERVOUS    SYSTEM.  141 


All  knowledge  acquired  and  communicated  by  nerves. 


eyes  upon  this  world,  you  see  a  being,  whose  senses  are  com- 
mencing their  work  as  inlets  of  knowledge  to  the  soul  within. 
Nothing  is  known  at  the  outset,  of  shapes,  or  colors,  or  dis- 
tances, or  any  other  relations  of  things.  This  is  all  to  be 
learned,  through  the  nerves  and  their  subordinate  organs.  And 
as  all  knowledge  is  acquired  through  the  nerves,  so  it  is  com- 
municated through  nerves  to  others.  It  is  communicated  by 
the  motions  that  are  excited  in  the  muscles  by  the  nerves — the 
motions  of  the  countenance  varying  its  expression  ;  the  motions 
of  the  limbs,  or  gestures  ;  but  especially  by  the  motions  which 
produce  and  articulate  the  voice.  Thought  and  feeling  can  be 
communicated  in  no  other  way  than  by  muscular  motion. 

223.  From  what  has  now  been  said,  you  readily  see,  what 
will  be  the  subjects  of  the  third  part  of  this  book.     They  are 
those  which  relate  to  the  nervous  system  and  its  connections  or 
dependencies.     They  are,  the  nervous  system  itself;  the  organs 
of  locomotion,  the  muscles,  and  the  bones ;  the  voice  ;  the  ex- 
pression of  the  countenance,  and  the  language  of  the  muscles 
generally  ;   the  senses,  with  their  organs ;    instinct ;  thought ; 
reason. 

224.  As  preparatory  to  a  particular  view  of  these  subjects,  I 
will  give  you  a  general  view  of  the  nervous  system,  with  the 
functions  performed  by  the  various  parts  of  it.     I  shall  reserve 
for  another  chapter  a  particular  view  of  some  of  the  higher 
functions  of  this  system,  and  a  consideration  of  some  subjects, 
which  we  can  better  examine  after  we  have  considered  the 
organs  of  locomotion  and  the  senses. 

225.  The    nervous    system  may  be    considered    as   having 
three  parts  ;  1,  certain  central  parts,  as  the  brain  and  spinal 
marrow ;   2,  nervous  trunks,  which  going  from  these  central 
parts  divide  and  subdivide,  as  the  arteries  do,  till  they  become 
exceedingly   minute ;    and   3,    the   nervous  expansion   in   the 
organs,  having  a  relation  to  the  nervous  trunks  similar  to  that 
which  the  capillaries  bear  to  the  arteries.     In  what  we  call  sen- 
sation we  suppose  that  an  impression  is  produced  in  the  nerv- 
ous expansion,  that  the  trunk  serves  to  transmit  it,  and  that 
through  the  nervous  centre,  the  brain,  it  is  communicated  to 
the  mind. 

226.  Let  us  see  now  what  is  necessary  to  this  compound  act, 
termed  sensation.     First,  it  is  necessary  that  the  organ  where 
the  nerve  is  expanded  be  in  a  condition  to  let  the  nerve  receive 
the  impression.     If  the  eye  be  so  injured  in  its  textures,  that 
the  impression  can  not  be  made  on  the  nerve,  there  can  be  no 


142  HUMAN  PHYSIOLOGY. 

Necessary  conditions  of  nervous  action  in  sensation  and  motion. 

vision.  So,  too,  of  the  other  senses.  Taste  and  smell  are  often 
impaired,  sometimes  even  destroyed  for  a  time,  by  an  inflam- 
mation of  the  mucous  membrane,  on  which  the  nerves  devoted 
to  these  senses  are  expanded.  This  is  sometimes  the  case  in  a 
common  cold.  It  is  necessary  also,  that  the  trunk  of  the 
nerve  be  in  a  proper  condition.  If  the  nerve  of  vision  be 
pressed  upon  by  a  tumor,  there  will  be  no  impression  trans- 
mitted from  the  images  formed  in  the  eye.  So,  too,  if  a  nerve 
going  to  any  part  of  the  body  be  cut  off,  there  can  be  no  trans- 
mission of  impressions  to  the  brain  from  that  part.  Again,  it 
is  necessary  to  sensation,  that  the  brain  should  be  in  a  state  to 
communicate  the  impression  to  the  mind.  If  the  brain  be 
pressed  upon  strongly  by  a  depression  of  the  skull  from 
violence,  or  by  effusion  of  blood  by  the  rupture  of  an  artery,  as 
sometimes  occurs  in  apoplexy,  there  can  be  no  sensation. 
Excitement  of  mind,  too,  sometimes  prevents  the  occurrence  of 
sensation,  by  its  action  upon  the  connection  between  the  mind 
and  the  brain.  The  pain  of  a  wound  received  in  battle  is  often 
unfelt,  until  the  excitement  of  the  battle  is  over.  The  aching 
of  a  tooth  is  often  stopped  by  the  excitement  consequent  upon 
going  to  the  dentist  to  have  it  extracted.  I  once  burned  my 
hand  in  the  beginning  of  a  chemical  lecture,  but  felt  no  pain 
till  I  had  finished  it,  and  then  the  pain  was  at  once  very 
severe.  In  these  cases  the  cause  of  the  pain  is  acting  all  the 
while  upon  the  nervous  extremity,  and  the  trunk  of  the  nerve 
is  capable  of  transmitting  the  impression,  but  the  state  of  the 
mind  is  such,  and  such  is  the  consequent  condition  of  the 
brain,  that  the  sensation  does  not  occur — one  link  in  the  neces- 
sary chain  is  defective. 

227.  The  same  can  be  said,  in  regard  to  the  necessity  of 
each  of  these  links  of  the  chain,  in  relation  to  voluntary  mo- 
tion, as  well   as  sensation.     The  brain  must  be  in  a  condition 
to  be   acted  upon  by  the  mind ;  the  nervous  trunk  must  be 
capable  of  transmitting  the  impression  ;  and  the  muscle  must 
be  in  such  a  state,  and  in  such  connection  with  the  extreme 
nervous  fibres,  that  it  can  respond  to  the  call  of  the  brain. 

228.  Before  going  further,  I  will  give  you  some  idea  of  the 
proportions  and  arrangement  of  the  central   organs   of  the 
nervous  system.     In  Fig.  72    you  have  presented  a   general 
view  of  this  system, — the  central  organs  with  the  nerves  going 
out  from  them.     At  a  is  the  cerebrum,  the  upper  large  brain, 
filling  up  a   considerable   portion   of  the  skull;    at   b  is  the 
cerebellum,  the  lesser  brain,  lying  beneath  the  cerebrum  at  its 


THE  NERVOUS  SYSTEM. 


143 


General  plan  of  the  nervous  system. 


FIG.  72. 


NERVOUS    TRUNKS    IN    MAN. 


144 


HUMAN  PHYSIOLOGY. 


Hemispheres  and  lobes  of  the  brain. 


back  part :  at  c  is  the  great  facial  nerve,  the  chief  nerve  of  the 
face ;  the  spinal  marrow,  c?,  sends  off  branches  on  either  side 
in  its  whole  length  ;  at  e  is  the  brachial  plexus,  a  bundle  of 
nerves  coming  from  the  spinal  marrow,  which  here  unite 
together,  and  are  then  distributed  to  all  parts  of  the  arm  ;  at  i 
is  a  similar  plexus  from  which  are  distributed  nerves  to  the 
lower  extremity ;  /,  #,  and  h  point  to  different  nerves  in  the 
arm,  and  I,  m,  n,  and  o  to  different  nerves  in  the  leg.  You 
observe  that  the  whole  of  this  nervous  system  is  divided  into 
exactly  similar  halves.  The  cerebrum  and  the  cerebellum  are 
both  double  organs,  and  the  nerves  of  one  side  are  just  like 
those  of  the  other. 

229.  Having  thus  observed  the  general  arrangement  of  the 
nervous  system,  I  call  your  attention  next  to  the  arrangement 
and  structure  of  the  brain  which  are  seen  in  Fig.  73.  This 


h  i  k  m     e 

BRAIN  AND  NERVES. 


Figure  presents  to  view  a  perpendicular  section  of  the  brain,  as 
made  from  front  to  rear,  dividing  it  into  two  halves.  You 
have  here  a  view  of  the  inner  surface  of  one  hemisphere,  as  it  is 


THE  NERVOUS  SYSTEM.  145 

Cerebrum.    Cerebellum.    Convolutions.    Membranes. 

termed,  of  the  cerebrum,  the  large  upper  brain,  which  is  com- 
monly described  as  having  three  lobes  or  divisions,  a,  the 
anterior ;  6,  the  middle ;  and  c  the  posterior.  At  /  is  the 
broad  band  of  white  fibrous  matter,  which  unites  the  two 
halves  or  hemispheres  together,  of  course  divided  in  the 
section  ;  at  d  is  the  cerebellum  showing  a  peculiarly  beautiful 
arrangement,  called  the  arbor  vitce,  or  tree  of  life ;  at  g  is  the 
beginning  of  the  optic  nerve  which  goes  to  the  eye ;  I  is  the 
nerve  of  smell ;  e  is  the  commencement  of  the  spinal  marrow. 
The  many  nerves  which  you  see,  are  distributed  to  various 
parts  of  the  face ;  the  nerve  at  h  goes  to  the  tongue ;  at  i  to 
the  throat,  and  at  m  to  one  of  the  muscles  of  the  eye.  From 
the  beginning  of  the  spinal  marrow  go  forth  many  nerves,  one 
of  which,  &,  is  a  very  important  one,  as  it  sends  off  branches  to 
the  lungs,  the  heart,  and  the  stomach.  It  is  this  part  of  the 
nervous  system,  the  top  of  the  spinal  cord,  that  it  is  most  im- 
mediately essential  to  the  continuance  of  life.  For  it  is  by 
their  nervous  connections  with  the  top  of  the  spinal  marrow, 
that  the  heart  and  lungs  continue  to  perform  their  duty.  It 
has  been  ascertained,  by  experiments  upon  animals,  that  the 
cerebrum,  and  even  the  cerebellum,  can  be  destroyed,  and  yet 
the  animal  will  continue  to  breathe,  and  the  circulation  will  go 
on  for  some  time.  But  the  moment  that  this  part  of  the 
spinal  cord,  from  which  the  heart  and  lungs  are  supplied  with 
nerves,  is  destroyed,  the  breathing  and  the  circulation  stop 
and  the  animal  dies.  So,  too,  in  apoplexy,  if  the  effusion  of 
blood  take  place  at  the  top  of  the  spinal  marrow,  death  will 
occur  more  certainly,  and  in  much  shorter  time,  than  if  the 
effusion  take  place  in  the  cerebrum  or  cerebellum. 

230.  You  observe  that  the  cerebrum  has  deep  irregular 
furrows  on  its  surface,  and  that  it  presents  undulating  tortuous 
projections.  These  are  called  the  convolutions  of  the  brain. 
Into  the  furrows  between  them  dips  down  the  membrane,  in 
which  branch  out  the  arteries  that  supply  the  brain  with  blood, 
and  the  veins  that  return  it  from  this  organ.  This  membrane 
is  from  its  soft  and  delicate  texture,  called  the  pia  mater  (pious 
mother),  while  the  stout  fibrous  membrane,  which  lies  outside 
of  this  next  to  the  bony  covering  is  called  the  dura  mater,  or 
hard  mother.  The  names  are  entirely  inappropriate,  for  the 
latter  serves  as  a  protection  to  the  brain,  and  the  former  is 
merely  a  vehicle  or  medium  for  the  entrance  of  the  blood 
vessels  into  the  brain.  There  is  another  membrane  lying 
between  these  which  is  called  the  arachnoid  membrane,  be- 
13 


146 


HUMAN"  PHYSIOLOGY. 


Gray  and  white  substance.    Proportions  and  arrangement. 

cause  in  its  tenuity  and  delicacy  it  resembles  the  spider's 
web.  It  is  one  of  the  serous  membranes,  and  it  serves  as  a 
protecting  envelope  to  the  brain,  and  at  the  same  time  by  its 
serum,  keeps  this  organ  bedewed  with  moisture  over  its  whole 
surface. 

231.  The  substance  of  which  the  brain  is  composed  is  very 
soft,  something  like  blanc-mange.  It  is  the  softest  organ  in 
the  body.  It  is  not  uniform  throughout  in  color.  All  around 
the  white  inner  part  of.  the  brain  there  is  a  thick  layer  of  gray 
substance.  In  Fig.  74  you  have  a  horizontal  section  of  the 

FIG.  74. 


SECTION  OF  THE  BRAIN. 


brain,  showing  the  proportions  and  arrangement  of  the  gray 
and  the  white  substances.  As  the  gray  substance  dips  down, 
as  you  see  in  the  figure,  into  all  the  furrows,  its  extent  is 
greater  than  you  would  suppose  at  the  first  view.  In  the 
middle  is  represented  the  broad  connection  which  exists 
between  the  two  hemispheres  of  the  brain.  You  observe  in 


THE  NERVOUS  SYSTEM. 


147 


The  gray  substance  made  of  cells,  the  white  of  tubes. 


Fig.  73,  and  Fig.  74,  that  there  is  no  apparent  arrangement  of 
the  external  parts  of  the  brain,  which  would  give  countenance 
to  the  idea  of  the  phrenologist,  in  relation  to  a  division  into 
particular  organs.  The  convolutions,  so  far  from  presenting 
any  well  defined  arrangement,  are  exceedingly  irregular. 

232.  The  gray  substance,  which  is   sometimes  called   the 
cortical  (bark-like)  substance,  because  it  surrounds  the  white 
central  part  of  the  brain,  is  made  up,  as  I  said  in  the  Chapter 
on  Cell-Life,  §  208,  of  cells,  while  the  white  part  is  composed  of 
exceedingly  minute  tubes.     These  tubes  are  continued  into  the 
nerves,  and  as  they  hold  the  nervous  matter,  they  constitute  the 
medium  of  communication  between  the  brain  and  all  parts  of 
the  body.     This  function  of  communication  is  the  sole  function 
of  the  white  nervous  matter.     In  the  brain  this  white  matter  is 
a  mere  collection  of  tubes,  and  these  branching  out  in  bundles 
form  the  nerves.      These  tubes  are  supposed  to  be  entirely 
separate  from  each  other,  from  their  beginning  in  the  brain  to 
their  termination  in   the  various  parts  of  the  body,  for  the 
microscope,  as  stated  in  §  205,  has  never  discovered  any  union 
between  them  at  any  point.     The  brain  then  is  a  great  central 
organ  of  communication,  where  innumerable  minute  tubes  are 
brought  together,  each  of  which  is  connected  with  some  one 
moving  fibre,  or  some  one  sensitive  point  in  the  body.     Those 
which  are  connected  with  mus- 
cular fibres   transmit   impres- 
sions  from    the    brain,    and 

those  which  are  connected 
with  sensitive  points  transmit 
impressions  to  it.  Of  the 
size  of  these  tubes  you  can 
judge  by  Fig.  75,  which 
shows  some  of  them  as  they 
appear  magnified  350  diam- 
eters. They  vary  much  in 
size,  but  the  cause  of  this 
variation  has  not  been  dis- 
covered. 

233.  The  office  of  the  gray 
substance,    it    is    quite    well 
ascertained,    is   very    different 
from   that  of  the  white  sub- 
stance,   as    the    difference    in 

its  structure  would  lead  us  to  suppose.     It  is  more  nearly 


FIG.  75. 


NERVOUS     TUBULI, 

Magnified  350  diameter*. 


148  HUMAN  PHYSIOLOGY. 

Office  of  the  gray  substance.     Proportioned  to  the  amount  of  intelligence. 

connected  with  the  mind  than  the  white  substance.  When, 
for  example,  motion  is  produced  in  obedience  to  the  will,  the 
impression  producing  the  motion  is  transmitted  through  the 
white  matter,  but  the  cause  of  this  impression  does  not  act 
directly  on  this  matter.  The  impression  is  caused  by  the 
action  of  the  mind  on  the  gray  matter,  and  the  white  substance 
only  serves  to  transmit  it.  The  gray  matter,  therefore,  has  a 
more  active  agency  than  the  white  in  the  phenomena  of  the 
mind  and  the  nervous  system.  It  is  the  first  link  in  the  chain 
of  connection  between  the  spiritual  and  the  physical  in  our 
nature.  Hence,  in  examining  the  brains  of  animals,  we  find 
that  the  higher  is  the  intelligence,  the  more  abundant  is  the 
gray  substance ;  and  it  is  especially  abundant  in  man,  by  the 
large  development  of  the  convolutions. 

234.  The  question  arises  here,  whether,  as  in  motion  the 
active  agency  is  on  the  part  of  the  gray  matter  in  the  brain, 
there  is  also  gray  matter  at  the  extremities  of  the  nerves  of 
sensation,  exerting  an  active  agency  there.  It  would  seem  that 
it  should  be  so.  When  voluntary  motion  is  produced,  the 
action  of  the  mind  is  on  the  gray  substance,  and  the  white  sub- 
stance of  the  brain  and  the  nerves  transmits  the  impression  of 
this  action.  But  in  sensation  the  first  step  in  the  process  is  not 
in  the  brain,  but  in  the  nervous  extremities.  Now  in  this  first 
step,  in  the  actual  production  of  the  impression  to  be  trans- 
mitted to  the  brain,  we  should  suppose  the  gray  matter  as 
necessary  as  in  the  production  of  the  impression  to  be  trans- 
mitted from  the  brain  in  effecting  voluntary  motion.  Else  we 
must  conclude,  that,  while  the  white  substance  can  have  no 
active  agency  in  the  brain,  but  serves  only  for  transmission,  at 
its  other  extremity,  expanded  in  the  organs,  it  serves  for  both 
transmission  and  production.  Dr.  Carpenter  supposes,  there- 
fore, that  there  is  a  sort  of  gray  matter  in  the  expanded  extrem- 
ities of  all  nerves  of  sensation.  But  the  microscope  has  never 
discovered  the  existence  of  this  matter  in  any  nervous  expan- 
sion, except  in  the  nerve  of  the  eye,  in  the  retina,  and  in  some 
parts  of  the  internal  ear.  And  some  facts  seem  to  militate 
against  Dr.  Carpenter's  view  of  the  subject.  If,  for  instance, 
you  hit  the  trunk  of  a  nerve,  as  the  little  nerve  so  often  hit  at 
the  elbow,  a  sensation  is  produced,  which  is  in  some  measure 
referred  to  the  part  to  which  the  nerve  is  distributed.  From 
such  facts  it  would  appear,  that  in  sensation  the  white  nervous 
matter  does  not  merely  transmit  impressions,  but  has  an 
agency  also  in  originating  them.  There  is  then  probably 


THE  NERVOUS  SYSTEM. 


149 


The  gray  substance  well  supplied  with  arterial  blood.     Ganglions  and  plexuses. 

no  gray  matter  ordinarily  in  the  expanded  extremities  of  a 
nerve,  but  they  are  merely  terminations  of  the  tubes  which 
make  up  its  trunk. 

235.  The  cells  which  form  the  peculiarity  of  the  structure  of 
the  gray  substance  are  often,  as  you  saw  in  Fig.  69,  of  very 
singular  appearance  from  their  prolongations.  They  lie  in  the 
interstices  of  a  vascular  network.  A  due  supply  of  arterial 
blood  is  absolutely  essential  to  the  vigorous  performance  of  the 
functions  of  the  gray  substance.  If  the  supply  be  cut  off  in 
any  way,  as  by  the  failure  of  the  heart's  action  in  fainting, 
insensibility  and  the  loss  of  the  power  of  motion  are  the  conse- 
quence. While  the  gray  substance  is  on  the  outside  of  the 
brain,  it  is  on  the  inside  of  the  spinal  marrow.  It  is  also  on 
the  inside  of  the  little  bodies  called  ganglions,  scattered  here 
and  there,  as  depositories  of  nervous  force,  or  as  little  brains,  as 
we  may  term  them.  These  ganglions  are  not  merely  a  part  of 
the  apparatus  of  communication.  They  are  different  from 
plexuses,  which  are  mere  combinations  of  nervous  trunks,  as 
seen  in  Fig.  77,  t  t  being  the  trunks,  which,  after  uniting  with 

FIG.  76. 


each  other  in  various  ways,  again  separate  to  go  to  their 
different  destinations.  At  g,  in  Fig.  76,  is  a  ganglion  into 
which  the  fibres  /  of  the  nerve  n  run.  It  then  divides  again 
into  branches  b.  These  ganglions  produce  nervous  force,  and 
therefore  are  composed  like  the  brain  in  part  of  gray  substance. 
The  spinal  marrow,  too,  produces  as  well  as  transmits,  and  so 

13* 


150  HUMAN  PHYSIOLOGY. 

Changes  in  the  nerve-cells.    Termination  of  the  nervous  fibres. 

this  substance  forms  a  part  of  it.  This  gray  substance,  as  it  is 
in  constant  operation,  is  subject  to  much  wear  and  tear,  as  we 
may  express  it,  and  therefore  the  changes  of  repair  are  con- 
stantly going  on  in  its  structure.  Hence,  the  necessity  for  so 
large  a  supply  of  blood,  as  is  secured  by  the  network  of  vessels, 
among  which  the  cells  peculiar  to  this  substance  are  scattered. 
The  microscope  has  fully  demonstrated  the  reality  of  these 
continual  changes,  for  it  shows  us,  whenever  a  portion  of  this 
substance  is  examined  by  it,  the  cells  in  all  the  various  stages 
of  development  mingled  together.  The  freshly  made  simple 
cells  are  seen  among  those  which  have  been  formed  for  some 
time,  and  which  have  put  forth  their  long  off-shoots,  as  seen  in 
Fig.  69. 

236.  The  extremities  of  the  fibres,  or  rather  of  the  tubuli 
(Fig.  75)  of  the  nerves  terminate  variously.  The  most  common 
termination  is  in  loops,  as  seen  in  Fig.  78,  which  represents  the 

FIG.  78. 


NERVES  OF  TOUCH  IN  THE  SKIN  OF  THE  THUMB. 

termination  of  the  nerves  as  seen  through  the  microscope  in 
a  thin  perpendicular  section  of  the  skin  in  the  thumb.  The 
three  eminences  in  this  figure  are  those  of  the  papilla,  as  they 
are  termed,  which  you  can  see  are  arranged  in  curvilinear  rows, 
if  you  look  at  the  ball  of  the  thumb.  In  Fig.  79  you  see  this 
same  loop-like  arrangement  in  the  nervous  tubuli,  as  seen 
through  the  microscope,  on  the  sensitive  sac  that  lines  the 
cavity  of  a  tooth,  the  entrance  for  the  nerves  and  bloodvessels 
of  this  sac  being  at  the  end  of  the  root, 

237.  One  very  singular  termination  of  the  nervous  tubuli,  is 
in  what  are  called  Pacinian  corpuscles,  after  Pacini,  the  first 
microscopist  that  discovered  them.  They  are  found  attached 
to  the  nerves  in  the  hand  and  foot  more  often  than  any  where 


THE  NERVOUS  SYSTEM. 


151 


Pacinian  corpuscles.    Their  office  not  known. 

FIG.  80. 


FIG.  79 


NERVES  IN  A  TOOTH. 


PACINIAN   CORPUSCLES. 


else.  Their  structure,  which  is  seen  in  Fig.  80,  A,  highly 
magnified,  is  very  curious.  They  are  attached  to  the  branches 
of  the  nerves  on  which  they  cluster  by  little  peduncles  or 
stalks.  At  a  is  the  peduncle;  6  is  the  nervous  fibre  or 
tubulus ;  /  is  its  termination  in  the  corpuscle.  The  corpuscle 
itself  is  composed  of  layers  of  a  very  delicate  fibrous  membrane 
inclosing  each  other  like  the  coats  of  an  onion,  to  the  number 
of  sometimes  sixty,  the  inner  ones,  d,  being  closer  together  than 
the  outer  ones,  c,  are.  In  B  is  represented  a  portion  of  a 
nerve  of  a  finger,  with  clusters  of  these  corpuscles  of  about  the 
natural  size.  Of  what  use  these  singular  bodies  are  we  know 
not.  But  the  fact  that  they  are  always  found  in  certain 
regions  of  the  body  shows  that  they  are  placed  there  for  some 
definite  purpose.  It  has  been  supposed  by  some  that  they  are 
minute  electrical  batteries,  because  they  bear  some  resemblance 
to  the  electrical  organs  found  in  some  fishes. 

238.  There  is  a  wonderful  fact  in  regard  to  the  healing  of 
wounded  nerves  which  must  not  pass  unnoticed.     You  know 


152  HUMAN  PHYSIOLOGY. 

Healing  of  nerves.     Nice  fitting  of  the  tubuli. 


that  if  a  nerve  be  divided,  all  communication  between  the  part 
that  it  supplies  with  branches  and  the  brain  is  cut  off.  No 
impressions  can  be  transmitted  through  it  to  and  from  the 
brain.  But  the  two  cut  ends  of  the  nerves  can  grow  together, 
and  the  communication  can  thus  be  more  or  less  restored. 
Sometimes  it  is  as  perfect  as  before.  Now,  if  you  call  to 
mind  the  structure  of  a  nervous  trunk,  you  will  see  that  this  is 
passing  wonderful.  It  is  made  up,  you  will  recollect,  of  tubuli 
which  are  entirely  separate  from  each  other,  and  each  one 
of  these  goes  from  its  origin  in  the  nervous  centre  to  its 
destination  by  itself.  It  is  difficult  to  conceive,  therefore,  how 
the  nerve  can  be  healed  without  creating  confusion.  For  to 
avoid  this  it  would  seem  to  be  necessary,  that  each  little  tube 
at  its  cut  end  must  unite  with  its  corresponding  end,  and  not 
with  the  end  of  some  tube  with  which  it  has  no  relation.  For 
example,  if  the  nerve  distributed  to  the  hand  were  cut,  it 
would  not  do,  as  it  seems  to  us,  to  have  tubuli  which  go  to  the 
thumb  unite  with  those  which  go  to  a  finger.  And  besides,  as 
I  shall  soon  show  you  that  the  tubuli,  through  which  the 
impression  that  produces  motion  is  transmitted,  are  separate 
from  those  which  transmit  the  impression  that  causes  sen- 
sation, it  would  not  do  for  a  tubulus  of  one  kind  to  unite 
in  the  healing  with  one  of  the  other  kind.  We  can  not 
conceive  how  a  confusion  in  sensations  and  motions  can  be 
avoided,  unless  the  end  of  each  fibre  or  tubulus  is  united 
with  its  corresponding  end ;  and  such  an  accurate  union 
of  the  multitude  of  tubuli  in  a  nerve  ^seems  an  impossibil- 
ity. That  there  is,  however,  a  very  accurate  union  effected,  is 
manifest  from  the  observations  of  M.  Brown  Sequard.  He 
examined  in  animals  nerves  which  were  divided  twelve  months 
before,  and  could  not  discover  the  point  of  division  even  with 
the  aid  of  the  microscope.  If  the  tubuli  were  not  all  made  as 
perfectly  continuous  as  before  the  nerve  was  divided,  the 
microscope  would  have  revealed  the  defect.  But  it  takes  time 
to  effect  this  adjustment  of  the  tubuli,  for  it  was  found  by  Dr. 
Haighton  in  his  experiments  nearly  fifty  years  ago,  that  after 
dividing  nerves,  their  functions  were  not  restored  till  some 
time  after  they  were  apparently  healed.  This  shows  most 
clearly,  that  the  arrangement  of  the  tubuli,  which  is  required 
for  the  communication  of  impressions  through  them,  is  gradu- 
ally effected  after  the  union  takes  place. 

239.  Taking  this  view  of  this  interesting  point,  the  difficulty 
is  greatly  enhanced,  when  we  look  at  the  union  of  parts  that 


THE  NERVOUS  SYSTEM.  153 

Nerves  of  the  spinal  morrow  compound. 

did  not  originally  belong  together,  as,  for  example,  when  a 
piece  of  skin  is  dissected  from  the  forehead,  and  is  twisted 
down  so  as  to  be  made  to  grow  on  to  the  nose  to  supply 
a  deficiency  4here.  Here  new  relations  entirely  are  established 
between  the  nerves  of  the  divided  parts,  and,  as  we  should 
expect,  there  is  confusion  in  the  sensations.  The  patient,  at 
first,  whenever  the  new  part  of  his  nose  is  touched  refers  the 
sensation  to  the  forehead.  But  this  confusion  of  the  sensations 
is  after  a  while  removed.  And  it  is  curious  to  observe,  that 
while  the  old  nervous  connections  are  breaking  up,  and  the 
new  ones  are  becoming  established,  there  is  an  interval  of 
partial,  sometimes  entire,  insensibility  in  the  part.  How  these 
new  relations  can  be  established  consistently  with  the  known 
arrangement  of  the  tubuli  in  the  nerves  is  a  mystery. 

240.  As  I  have  already  hinted,  there  are  different  nerves  for 
different  purposes.  The  nerves  through  which  the  mind  sends 
its  messages  to  the  muscles,  are  not  the  same  with  those 
through  which  it  receives  impressions  in  sensation.  In  and 
about  the  face,  the  nerves  of  motion  and  sensation  are,  for  the 
most  part,  entirely  separate  from  each  other.  But  in  other 
parts  of  the  body,  the  fibres  or  tubuli  for  motion  and  sensation 
are  mingled  together  in  the  same  nervous  trunk,  inclosed  in 
one  sheath.  It  is  found  that  each  of  the  nerves,  coining  out 
from  each  side  of  the  spinal  marrow,  has  two  roots,  which 
unite  together  and  are  inclosed  in  one  sheath. 
This  arrangement  is  represented  in  Fig.  81, 
in  which  a  is  a  portion  of  the  spinal  cord ; 
d  the  anterior  root ;  6  the  posterior  root ;  e 
the  trunk  formed  by  the  union  of  these  two 
roots ;  and  /  a  branch  of  the  nerve.  At  c, 
on  the  posterior  root  is  one  of  the  ganglions,  or 
little  brains,  of  which  I  spoke  in  §  235. 
Why  they  are  placed  on  these  posterior  roots, 
and  not  on  the  anterior,  or  why  they  are 
placed  here  at  all,  we  know  not.  It  has 
been  ascertained  by  many  experiments  on 
animals,  that  the  posterior  roots  are  composed 
of  tubuli,  which  bring  impressions  to  the  -spinal  marrow ;  while 
the  anterior  are  composed  of  tubuli  which  carry  impressions 
from  the  spinal  marrow.  For,  if  the  spinal  cord  of  an  animal 
be  laid  bare,  and  a  posterior  root  be  irritated,  pain  is  produced ; 
but  if  an  anterior  root  be  irritated,  violent  motions  are  caused 
in  the  parts  to  which  the  nerve  is  distributed.  That  is,  the 


154  HUMAN  PHYSIOLOGY. 

Different  nerves  for  different  offices. 

posterior  root  is  a  nerve  of  sensation,  and  the  anterior  a  nerve 
of  motion.  It  is  a  mere  matter  of  convenience  that  they  unite, 
and  are  mingled  together  in  the  same  sheath,  for  they  are  to 
be  distributed  in  the  same  parts.  In  and  about^he  face  the 
nerves  of  motion  and  sensation  are  kept  for  the  most  part 
separate,  as  before  stated,  merely  because  it  would  be  no  con- 
venience in  any  case  to  put  them  together  in  one  sheath. 

241.  But  not  only  are  there  different  nerves  for  sensation 
and  for  motion,  but  there  are  also  different  nerves  for  different 
kinds  of  sensation.     Thus,  in  the  eye,  the  optic  nerve  which 
transmits  the  impressions   from   the   images   formed   on    the 
retina,  as  will  be  shown  in  the  Chapter  on  the  Eye,  is  wholly 
separate  from  the  nerve  by  which  any  pain  or  irritation  is  felt 
in  this  organ.     The  latter  is  called  a  nerve  of  common  sen- 
sation— the  former  a  nerve  of  special  sensation.     So  in  the 
nose,  the  nerve  that  takes  cognizance  of  odors  is  a  different 
one  from  that  by  which  irritation  on  the  same  membrane  is 
felt.     The  snuff-taker  smells  the  snuff  with  one  nerve,  and  feels 
its  tingling  with  another. 

242.  The  nerves  devoted  to  one  kind  of  sensation  can  not  in 
any  case   perform  the  function  of  those  of  any  other  kind. 
Each  nerve  is  fitted  for  its  own  peculiar  office,  and  has  for  this 
its  own  peculiar  susceptibility.     Thus,  the  nerve  of  touch  is 
insensible  to  light,  and,  on  the  other  hand,  the  nerve  of  vision 
is  insensible  to   touch.     If,  therefore,  the  nerve  of  vision  be 
paralyzed,  but  the  nerve  of  common  sensation  in  the  eye  be 
unimpaired,  although  there  is  no  seeing,  the  eye  is  as  sensible 
to  irritation  as  ever.     On  the  other  hand,  if  the  nerve  of  vision 
be  unimpaired,  and  the  nerve  of  common  sensation  be  par- 
alyzed, as  sometimes  happens,  the  individual  can  see,  but  he 
has  lost  the  sentinel  that  stands  guard  over  the  eye,  and  by  its 
warning  of  pain  keeps  it  from  injury.      What,  therefore,  is 
flying  in  the  atmosphere  may  lodge  in  the  eye,  and  though  it 
produce  no  pain,  it  will  excite  inflammation  by  irritating  the 
capillaries.      The   eye   in   some  of  these   cases  is  destroyed, 
by  the  inflammation  which  thus  arises  from  the  loss  of  sensi- 
bility to  the  touch.     When  the  nerve  of  common  sensation  is 
in  a  healthy  state,  the  moment  any  thing  gets  into  the  eye 
great  pain  is  produced,  and  the  tears  flow  and  the  eyelids  are 
in  constant  motion ;  and  if  by  these  instinctive  means,  as  we 
may  term  them,  the  irritating  substance  is  not  removed,  other 
means  are  at  once  resorted  to.     But  when  this  nerve  is  par- 
alyzed, although  the  irritating  substance  produces  no  pain,  it 


THE  NERVOUS  SYSTEM.  155 

Different  degrees  of  sensibility  in  the  various  parts  of  the  body. 

gradually  causes  inflammation  in  the  delicate  vascular  texture 
of  the  eye.  Pain,  then,  in  this  case,  as  well  as  in  every  other, 
is  a  safeguard  against  danger.  The  part  is  endowed  with  an 
acute  sensibility  to  touch,  because  it  is  needed  as  a  sentinel  in  a 
part  so  delicate  and  yet  so  exposed. 

243.  This  leads  me  to  remark,  that  the  different  parts  of  the 
body  are  endowed  with  different  degrees  of  sensibility,  accord- 
ing to  their  necessities,  in  relation  to  the  warning  of  danger. 
Accordingly,  the  skin  is  the  most  sensitive  part  or  organ  of  the 
body,  that  it  may  warn  at  once  of  the  approach  of  danger ; 
while  the  internal  parts  have  much  less  sensibility,  some  of 
them  none.     In  the  performance  of  operations,  therefore,  the 
great  suffering  is  in  the  cutting  of  the  skin.     There  is  very 
little  sensibility  in  the  muscles,  and  there  is  none  in  the  bones. 
The  following  fact  illustrates  the  use  of  the  sensibility  of  the 
skin  in  the  prevention  of  injury.     A  man  who  had  lost  all 
sensibility  in  his  right  hand,  but  retained  the  power  of  motion, 
lifted  the  cover  of  a  pan  when  it  was  burning  hot.     Although 
he  was  not  aware  of  any  effect  at  the  moment,  the  consequence 
was  the  loss  of  the  skin  of  the  fingers  and  of  the  palm  of  the 
hand,  laying  bare  the  muscles  and  tendons.     If  the  sensibility 
had  not  been  lost,  that  is,  if  the  nervous  tubuli  which  transmit 
sensation  had  not  been  paralyzed,  the  warning  of  pain  would 
have  been  instantly  given  to  the  brain,  and  orders  would  have 
been  sent  to  the  muscles  to  relax  their  grasp  of  the  cover ;  and 
so  rapid  are  these  transmissions,  that  the  cover  would  have 
been  dropped  soon  enough  to  prevent  any  great  amount  of 
injury  from  being  done. 

244.  Although  there  is  so  little  sensibility  in  the  internal 
parts  in  their  healthy  condition,  yet  when  they  become  inflamed 
they  become  sensible  of  pain,  sometimes  acutely  so.     Thus,  an 
inflamed  bone  is  the  seat  of  severe  pain ;  and  the  tendons, 
although    nearly    insensible    ordinarily,  become  very   painful 
when  inflamed,  as  any  one  that  has  a  deep-seated  felon  can 
testify.     The  question  as  to  the  cause  of  this  change  of  sen- 
sibility I  will  not  stop  to  discuss,  but  that  there  is  a  benevolent 
object  in  it  is  very  manifest.     If  inflammation   caused  no  pain 
in  such  parts,  it  might  go  on  to  a  destructive  extent  without 
the  person's  being  aware  of  the  danger,  and  therefore  without 
his  applying  for  medical  means. 

245.  It  was  formerly  supposed  that  a  nerve  must  of  course 
have  an  exquisite  sensibility.     But  there  is  no  sensibility  in 
nerves  devoted  to  motion.     Neither  is  there  any  in  the  brain 


156  HUMAN  PHYSIOLOGY. 


Insensibility  of  the  heart  to  the  touch.    Respiratory  nerve  of  the  face. 

itself.  Portions  of  it  can  be  cut  off  without  producing  any 
pain.  The  heart,  too,  is  insensible  to  the  touch.  A  case 
proving  this  fell  under  the  observation  of  Harvey,  the  dis- 
coverer of  the  circulation  of  the  blood.  A  young  nobleman, 
from  an  injury  received  in  a  fall,  had  a  large  abscess  on  the 
chest,  which  occasioned  such  a  destruction  of  the  parts,  as  to 
leave  the  lungs  and  heart  exposed.  Charles  L,  on  hearing  of 
the  case,  desired  to  have  Harvey  see  it.  "When,"  says 
Harvey,  "I  had  paid  my  respects  to  this  young  nobleman,  and 
conveyed  to  him  the  king's  request,  he  made  no  concealment, 
but  exposed  the  left  side  of  his  breast,  when  I  saw  a  cavity, 
into  which  I  could  introduce  my  fingers  and  thumb ;  aston- 
ished with  the  novelty,  again  and  again  I  explored  the  wound, 
and  first  marveling  at  the  extraordinary  nature  of  the  case,  I 
set  aboiit  the  examination  of  the  heart.  Taking  it  in  one 
hand,  and  placing  the  finger  on  the  wrist,  I  satisfied  myself 
that  it  was  indeed  the  heart  which  I  grasped.  I  then  brought 
him  to  the  king,  that  he  might  behold  and  touch  so  extraordi- 
nary a  thing,  and  that  he  might  perceive,  as  I  did,  that  unless 
when  we  touched  the  outer  skin,  or  when  he  saw  our  fingers 
in  the  cavity,  this  young  nobleman  knew  not  that  we  touched 
his  heart!"  This  absence  of  sensibility  in  the  heart  is  not 
because  it  is  not  well  endowed  with  nerves.  It  is  well 
endowed,  but  it  is  with  nerves  which  are  devoted  to  another 
purpose.  They  are  nerves  of  sympathy,  which  establish  a 
connection  with  every  part  of  the  body,  making  this  organ  to 
be  so  easily  affected  by  motion,  by  disease,  and  by  every  pass- 
ing emotion  in  the  mind. 

246.  In  the  face  we  have  an  example  of  different  sets  of 
nerves  for  different  classes  of  motions.  All  those  motions  that 
are  used  in  the  expression  of  the  countenance  are  associated 
together  by  a  certain  nerve.  This  nerve  has  nothing  to  do 
with  other  motions,  as  mastication.  Other  nerves  are  provided 
for  them.  Sometimes  this  nerve  of  expression  is  paralyzed  on 
one  side.  The  result  is,  that  while  the  individual  can  masti- 
cate equally  well  on  both  sides,  he  can  laugh,  and  cry,  and 
frown,  only  on  one  side,  and  he  can  not  close  the  eye  on  the  side 
affected.  In  Fig.  82  is  a  representation  of  this  condition  of 
things.  The  left  eye  can  not  be  closed  by  any  effort,  and  the 
left  side  of  the  face  is  wholly  devoid  of  expression.  This  nerve 
of  expression  is  often  paralyzed  by  itself,  the  other  nerves  in  the 
neighborhood,  both  nerves  of  sensatioti  and  of  motion,  being 
entirely  unaffected.  This  nerve  has  been  called  the  respiiatory 


THE   NERVOUS  SYSTEM. 


157 


Paralysis  of  the  respiratory  nerve  of  the  face. 


FIG.  82. 


PARALYSIS    OF    THE    NERVE    OF    EXPRESSION 

on  one  side  of  the  face. 

nerve  of  the  face,  because  it  controls  motions  which  are  con- 
nected with  the,  movements  of  respiration.  If  you  observe  how 
the  various  passions  and  emotions  are  expressed,  you  will  sea 
that  there  is  a  natural  association  between  the  muscles  of  the 
face  and  those  of  the  chest  in  this  expression.  This  is  very 
obvious  in  laughing  and  in  weeping.  But  this  association  can 
be  effected  only  through  nervous  connections.  And  these  con- 
nections in  this  case  are  very  extensive  and  intimate.  When 
the  nerve  of  expression,  or  facial  respiratory  nerve,  is  par- 
alyzed, all  the  motions  of  the  face  connected  with  the  respi- 
ration are  absent.  Though  the  individual  may  sob  in  weep- 
ing, or  send  forth  the  rapid  and  successive  expirations  of 
laughter,  yet  the  face  on  the  side  where  the  nerve  is  par- 
alyzed will  be  perfectly  quiescent.  So,  too,  those  movements 
of  the  nostrils  which  are  sometimes  used  in  expression,  can 
not  be  performed.  Sneezing  and  sniffing  up  can  not  be  dono 

14 


158  HUMAN   PHYSIOLOGY. 

Nerves  of  the  eye.     Paralysis  affecting  different  nerves. 

on  the  affected  side.  Neither  can  the  individual  whistle, 
because  a  branch  of  this  nerve  goes  to  the  muscles  at  the 
corner  of  the  rnouth,  which  are  therefore  disabled.  Sir 
Charles  Bell,  in  cutting  a  tumor  from  before  the  ear  of  a 
coachman,  divided  this  branch  of  the  nerve.  Shortly  after,  the 
man  thanked  him  for  curing  him  of  a  formidable  disease, 
but  complained  that  he  could  no  longer  whistle  to  his  horses. 

247.  The  eye  has  six  different  nerves,  each  for  a  different 
service.     1.  The  optic  nerve.     This  has  nothing  to  do  with  the 
motions  or  the  common  sensations  of  the  eye.     Its  sole  office  is 
to  transmit  impressions  from  the  images  formed  in  the  eye  to 
the  brain.     2.  A  nerve  of  common  sensation,  by  which  any  irri- 
tation in  the  eye  is  felt.     3.  A  nerve  which  is  distributed  to  the 
muscles  of  the  eye  generally,  and  to  no  other  parts  of  this  organ. 
4.  A  nerve  which  goes  to  one  particular  muscle,  one  of  the  oblique 
muscles  of  the  eye.     It  is  an  involuntary  muscle  which  performs 
the  insensible  rolling  motions  of  the  eyeball,  and  is  associated 
with  the  muscles  of  expression  in  the  countenance  by  means  of 
nervous  connections.     5.  A  nerve  which  goes  to  another  single 
muscle,  which  turns  the  eye  outward.     6.  A  branch  of  the 
respiratory  nerve,  which  regulates  the  motion  of  the  eyelids, 
and  has  much  to  do,  therefore,  with  the  expression  of  the  coun- 
tenance.    To  this  small  organ,  then,  are  distributed  six  different 
nerves,  each  having  its  distinct  office,  and  its  separate  origin  in 
the  brain.     How  various  are  the  transmissions  through  these 
nerves,   and  how  nicely  adjusted  must  all  the  parts  of  this 
complicated   apparatus    be,  that   each  may  perform  its  office 
without  interference  with  the  rest ! 

248.  I  have  already  alluded  incidentally  to  the  fact,  that  one 
nerve  may  be  paralyzed,  and  others  distributed  to  the  same 
parts  may  be  entirely  unaffected.     Thus  the  nerve  of  expression 
in  the  face  may  be  paralyzed  alone,  the  face  retaining  its  usual 
sensibility  and  its  power  of  performing  other  motions  than  those 
of  expression,  as  mastication,  because  the   nerves  of  common 
sensation  and  of  common  motion  are  untouched  by  the  disease. 
So,  too,  in  the  nerves  which  go  out  from  the  spinal  marrow, 
composed  of  tubuli  of  motion  and  sensation  mingled  together, 
one  set  of  the  tubuli  may  be  affected  while  the  other  is  not ; 
for  in  paralysis  it  is  often  the  case  that  the  sensibility  remains 
while  the  power  of  motion  is  gone,  and  vice  versa.     Sir  Charles 
Bell   relates  an  interesting  case,  in  which  the  paralysis  was 
different  on  the  two  sides  of  the  body.     A  mother  was  seized 
with  a  paralysis,  in  which  there  was  a  loss  of  muscular  power 


THE  NERVOUS  SYSTEM.  159 


Nerves,  though  having  different  offices,  all  alike  in  structure. 

on  one  side,  and  a  loss  of  sensibility  on  the  other.  She  could 
hold  her  child  with  the  arm  of  the  side  which  retained  its 
power  of  motion  but  had  lost  its  sensibility.  But  she  could  do 
it  only  when  she  was  looking  at  it.  She  could  not  feel  her 
child  on  the  arm,  and  therefore  when  her  attention  was  drawn 
to  any  thing  else,  and  she  ceased  to  have  her  eyes  fixed  on  the 
child,  the  muscles  having  no  overseer,  as  we  may  say,  to  keep 
them  at  work,  were  relaxed  at  once,  and  the  child  would  fall 
from  her  arm.  In  this  case,  bound  up  in  the  same  sheaths  were 
two  sets  of  tubuli,  one  set  of  which  were  useless  in  the  nerves 
on  one  side  of  the  body,  and  the  other  set  were  useless  in  the 
nerves  of  the  other  side. 

249.  We  should  suppose  that  there  would  be  a  difference  in 
the  construction  of  the  nerves,  corresponding  with  the  different 
uses  to  which  they  are  devoted.     But  it  is  not  so.     The  micro- 
scope shows  us  that  the  nerves  of  motion  and  of  common  and 
special  sensation  are  all  alike  in  their  structure,  and  chemistry 
shows   us  that  they  are  alike  also  in  their  composition.     The 
question  arises,  then,  why  the  impression  producing  motion  can 
not  be  transmitted   by  the  same   nerve  with  the  impression 
causing  sensation.     The  reason  is  evidently  not  to  be  found  in 
the  nervous  trunk  itself,  as  this  is  the  same  in  all  cases.     It  is 
in  the  circumstances  of  the  two  ends  of  the  nerve — that  which 
is  in  the  nervous  centre  from  whence  it  arises,  and  that  which 
is  expanded  in  some  part  of  the  body.     You  can  see  at  once 
that  the  nervous  tubuli  which  end  in  the  fibres  of  a  muscle 
can  not  transmit  sensation  to  the  brain  from  the  skin  over  the 
muscle,  because  they  do  not  go  to  the  skin  at  all.     There  are 
other  tubuli  that  are  distributed  there  for  that  purpose,  mingled 
indeed  in  most  cases  with  the  tubuli  for  motion,  but  yet  kept 
entirely  distinct  from  them.     And  besides,  there  is  probably 
something  in  the  mode  of  arrangement  of  the  extremities  of  a 
nerve  of  sensation,  which  differs  from  that  which  exists  in  the 
distribution  of  a  nerve  of  motion,  so  as  to  make  it  impossible 
for  a  nerve  of  motion  to  receive  the  impression  producing  sen- 
sation, even  where  the  impression  is  made  directly  upon  the 
muscle  itself.      There  is  also  probably  a  different  ending  of  the 
nerves  of  sensation  and  motion  in  the  nervous  centre,  the  brain, 
or   spinal    marrow,  that    makes    the   one    kind    incapable  of 
performing  the  duties  of  the  other  kind. 

250.  There  have  been  many  hypotheses  in  regard  to  the 
action   of  the  nerves.     The  most  common  theory,  even  up  to 
modern  times,  was  this — that  the  brain  is  not  only  the  great 


160  HUMAN   PHYSIOLOGY. 

Nerve-force  not  electricity.    Proved  by  facts  and  experiments. 

centre  of  the  nervous  system,  but  its  central  workshop,  as  \re 
may  express  it,  and  that  in  it  is  secreted  a  nervous  fluid,  which 
is  distributed  through  all  the  body  by  the  nerves,  they  being, 
as  it  was  supposed,  bundles  of  conduit-pipes.  This  fluid  was 
supposed  to  move  back  and  forth  in  the  nerves,  going  outwards 
towards  the  extremities  of  the  nerves  to  excite  motion,  and 
going  inward  to  the  brain  to  convey  the  sensation  of  external 
impressions.  This  theory  has  been  exploded  by  the  researches 
of  Sir  Charles  Bell  and  others,  and  during  the  last  half  century 
important  and  numerous  discoveries  have  been  made,  in  rela- 
tion to  the  functions  of  different  parts  of  the  nervous  apparatus. 
And  though  there  are  many  things  in  this  system,  which  links 
the  spiritual  with  the  physical,  that  we  shall  never  understand, 
the  bounds  of  our  knowledge  in  regard  to  it  are  undoubtedly 
to  be  largely  widened  by  future  researches. 

251.  It  is  a  favorite  idea  with  some  physiologists  that  nerve- 
force,  as  it  is  termed,  is  identical  with  electricity,  and  that  the 
nervous  system  is  therefore  a  system  of  electrical  batteries,  with 
an  apparatus  for  a  sort  of  telegraphic  communications.  They 
ground  their  opinion  upon  the  fact,  that  a  current  of  electricity 
passed  along  nerves  may  produce  motion  or  sensation,  accord- 
ing to  the  character  of  the  nerve  through  which  it  is  passed, 
and  also  upon  the  analogy  which  exists  between  nerve-force 
and  electricity  in  the  instantaneousness  of  their  transmission. 
But  facts  and  experiments  have  wholly  disproved  this  alleged 
identity.  Some  of  these  I  will  briefly  relate.  Mechanical  and 
chemical  stimuli  produce  the  same  nervous  action  that  elec- 
tricity does.  This  shows  that  the  electricity  acts  merely  as  a 
stimulus  to  wake  up  the  nerve-force,  instead  of  being  that  force 
itself.  Experiments  have  been  tried,  to  detect,  if  possible,  the 
existence  of  an  electrical  current  in  a  nervous  trunk  while  the 
parts  to  which  it  is  distributed  were  in  action,  but  in  vain. 
Thus,  Prof.  Matteucci  laid  bare  the  large  nerve  of  the  leg  of  a 
horse,  and  although  by  irritating  its  roots  he  excited  powerful 
action  of  the  muscles  of  the  leg,  the  instrument  in  connection 
with  the  nerve  was  entirely  unaffected,  though  it  was  so  ex- 
tremely delicate  that  it  would  indicate  an  infinitesimally  small 
disturbance  of  the  electrical  equilibrium.  Again,  a  ligature  put 
around  a  nerve  will  by  its  compression  prevent  nervous  trans- 
mission through  it,  but  will  not  hinder  the  passage  of  an  elec- 
trical current.  Still  again,  if  a  piece  of  a  nerve  be  cut  out,  and 
some  good  conducting  substance  be  introduced  in  its  place,, 
electricity  will  pass,  but  there  can  be  no  transmission  of  nerve 


THE  NERVOUS  SYSTEM.  161 


Products  of  nervous  action— sensation,  motion  voluntary  and  involuntary. 

force  to  the  parts  below  the  division.  Besides  all  this,  nerve- 
force  differs  from  electricity  in  the  fact  that  it  can  be  confined 
to  the  nervous  trunk,  or  even  to  a  small  portion  of  the  trunk,  as 
when  a  motion  is  very  limited  in  extent ;  while  electricity  not 
only  passes  through  the  whole  trunk,  to  all  the  parts  to  which 
the  nerve  is  distributed,  but  is  diffused  in  the  parts  around  it. 
Thus,  if  an  electrical  current  be  passed  through  the  main  nerve 
of  the  limb  of  an  animal,  it  will  go  through  every  branch 
of  that  nerve,  and  cause  all  the  muscles  of  the  limb  to  contract ; 
but  nerve-force  may  be  so  insulated  in  a  small  portion  of  the 
nerve,  that  a  single  toe  may  be  moved  alone.  And  some  of  the 
electricity  will  be  diffused  at  once  in  the  muscles  and  other 
parts  around  the  trunk  of  the  nerve  before  it  reaches  any  of  the 
branches  that  go  off  from  it.  Indeed,  the  muscles  are  much 
better  conductors  of  electricity  than  the  nerves,  which  should 
not  be  if  the  nerves  were  particularly  designed  for  its  transmis- 
sion, as  the  hypothesis  would  claim.  And  both  muscles  and 
nerves  are  nothing  like  as  good  conductors  as  a  common  copper 
wire. 

252.  We  have  thus  far  contemplated  nervous  action,  for 
the  most   part,  only  in  two  forms — as   producing   sensation 
and  voluntary  motion.      In  sensation  the  action  is  from  the 
extremity  of  the  nerve  to  the  nervous  centre ;  but  in  motion  it 
is  from  the  centre  to  the  extremities  of  the  nerves,  as  they  are 
expanded  among  the  fibres  of  the  muscles.      This  voluntary 
motion,  you  see,   may  arise  in  consequence  of  sensation,  as 
when  you  withdraw  the  hand  from  the  fire,  if  the  heat  be 
painful;   or  it  may  occur  without  a  preceding  sensation,  as 
when  the  thinking  mind  wills  to  perform  certain  motions  for 
effecting  some  purpose.     In  either  case  it  is  supposed  that  the 
gray  vesicular  or  cellular  substance  of  the  brain  is  in  immediate 
connection  with  the  mind,  and  that  the  white  tubular  matter 
of  the  brain  and  the  nerves  serves  only  for  transmission.     That 
is,  both  in  sensation  and  motion  the  effective  physical  agency  is 
in  the  vesicular  gray  substance.     This  is  the  working  part  of 
the  telegraphic  apparatus  of  the  mind,  while  the  innumerable 
tubuli  of  the  white  matter  of  the  brain  and  nerves  are  the 
communicating  wires. 

253.  Much  of  the  muscular  motion  of  the  body  is  produced 
without  the  agency  of  the  will,  and  sometimes  even  in  oppo- 
sition to  it.     This  is  true  of  the  motions  caused  by  emotions  in 
the  mind.     For  example,  the  muscular  motions  in  sobbing  and 
in  laughing  often  occur  in  opposition  to  the  strong  action  of  the 

14* 


162  HUMAN   PHYSIOLOGY. 

Involuntary  motion.     Excitor  and  motor  nerves. 

will.  In  this  case,  the  emotion  produces  its  effect  upon  the  gray 
vesicular  substance,  and  from  this  the  impression  is  transmitted 
through  the  nerves  to  the  muscles. 

254.  There  are  some  common  motions  which  are  performed 
to  a  greater  or  less  extent  without  the  agency  of  the  will.     The 
muscles  which  perform  them  are  called  involuntary  muscles. 
The  muscles  of  respiration,  for  example,  ordinarily  act  without 
our  willing  them  to  do  so.     If  they  did  not,  respiration  would 
stop  when  we  sleep,  or  become  stopped  from  disease.     But  the 
•will   can   quicken  these  muscles  in   their  action.      They  are 
therefore  not  wholly  involuntary.     But  there  are  some  purely 
involuntary  muscles.     The  muscular  coat  of  the  stomach,  which 
I  spoke  of  in  the  Chapter  on  Digestion,  as  being  constantly  in 
motion  when  the  stomach  is  filled  with  food,  is  of  this  char- 
acter.    No  effort  of  the  will  can  quicken  or  retard  the  action  of 
this  muscle.     That  exceedingly  compound   muscular   engine, 
the  heart,  is  a  collection  or  arrangement  of  purely  involuntary 
muscles.      No   effort   of  the   will   can    directly   influence   its 
motions,  though  it  may  do  it  indirectly,  by  so  directing  the 
thoughts  as  to  awaken  emotions  calculated  to  produce  this 
effect.     That  beautiful  circular  curtain  in  the  eye,  the  iris,  has 
the  size  of  its  circular  opening,  the  pupil,  controlled,  as  you  will 
see  in  the  Chapter  on  the  Eye,  by  an  involuntary  muscle. 

By  what  agency,  you  will  inquire,  are  these  involuntary 
motions  produced  ?  The  answer  to  this  question  will  open  to 
you  a  new  view  of  the  nervous  system. 

255.  I  have  already  alluded  to  the  two  roots  which  unite  to 
make  up  each  nerve  that  comes  from  the  spine.     One  of  these 
roots  is  composed  of  tubuli  through  which  impressions  are 
transmitted  to  the  spinal    marrow ;    and  the  other  contains 
tubuli,  through  which  an  impression  is  transmitted  from  the 
spinal  marrow  to  the  muscles,  causing  them  to  contract.     Each 
nerve,  then,  coming  from  the  spine,  is  made  up  of  two  distinct 
nerves,  or  two  distinct  sets  of  tubuli.     One  of  these  is  called  an 
excitor  nerve,  the  other  a  motor  nerve.     In  the  case  of  the 
muscles  of  respiration,  every  time  that  they  act,  the  process  is 
this — an  impression  is  transmitted  from  the  lungs  through  an 
excitor  nerve  to  the  spinal  marrow,  the  gray  vesicular  substance 
there  responds  to  this  impression,  and  sends  in  consequence  an 
impression  by  a  motor  nerve  to  the  muscles.     So  in  the  case 
of  the  iris,  which  contracts  to  prevent  too  much  light  from 
entering  the  eye,  the  light  as  it  strikes  the  retina  produces  an 
impression,  which  is  transmitted  through  an  excitor  nerve,  an(J 


THE  NEKVOTJS   SYSTEM.  163 

Reflex  action  of  nerves.    Sometimes  sensation  with  it,  and  sometimes  not. 

in  consequence  another  impression  is  transmitted  through  a 
motor  nerve  to  the  iris.  So  also,  the  presence  of  food  in  the 
stomach  produces  an  impression  which  is  transmitted  through 
the  excitor  nerve,  and  another  impression  is  returned  through 
the  motor  nerve,  exciting  the  muscular  coat  to  action.  And  in 
the  act  of  swallowing  an  impression  is  transmitted  from  the 
food  thrust  back  into  the  throat,  and  then  impressions  are 
returned  to  the  many  muscles  engaged  in  this  compound  act, 
(§  78).  The  action  of  the  nerves  illustrated  by  these  examples 
is  termed  their  reflex  action,  because  the  impression  transmitted 
by  one  nerve  to  the  spinal  marrow  is  reflected  from  it  by 
another. 

256.  You  see  that  I  use  the  rather  indefinite  word,  impres- 
sion, in  relation  to  the  transmissions  through  the  nerves.     It  is 
the  best  word  that  can  be  employed,  because  although  some- 
thing is  transmitted,  we  know  not  what  that  something  is. 
The  result  of  the  transmission  is  different  in  the  excitor  nerve 
from  what  it  is  in  the  motor  nerve.     The  result  differs  also  in 
the  excitor  nerves  according  to  circumstances.     In  some  cases 
it  is  accompanied  with  actual  sensation,  while  in  others  it  is 
not.     That  is,  the  brain  sometimes  participates  in  the  result, 
and  sometimes  it  is  confined  to  the  spinal  marrow.     Thus,  in 
the  act  of  respiration,  the  impression  carried  from  the  lungs  by 
the  excitor  nerves  comes  from  the  presence  of  dark  blood  in  the 
lungs.     Ordinarily,  a  mere  impression,  and  nothing  like  sen- 
sation, is  transmitted.     The  respiratory  muscles,  most  of  the 
time,'  go   on   to   do    their  work,  in  obedience  to  the  impres- 
sions communicated  from  the  lungs,  without  the  process  being 
recognized  by  the  mind.     But  when  there  is  embarrassment 
in  the  lungs,  the  quiet  process,  carried  on  through  the  agency 
of  the  spinal  marrow  alone,  is  not  adequate  to  meet  the  exi- 
gency.    In  some  way,  the  brain  becomes  a  party  in  the  ope- 
ration.    The  act  of  breathing  is  now  accompanied  with  pos- 
itive sensations,   and    there  is  a   mixture    of   voluntary    and 
involuntary  muscular  action.     So,  also,  the  ordinary  movements 
of  the  stomach  are  attended  with  no  positive  sensations.     That 
is,  there  is  no  transmission  to  the  brain  of  any  impression  of 
which  the  mind  takes  cognizance.     But  if  there  be  disturbance 
there,  and  extraordinary  movements  are  produced,  then  cogni- 
zance is  taken  of  them,  and  sensations  of  various  kinds  result. 

257.  The   spinal   marrow,   in    relation  to    the    involuntary 
muscles,  seems  ordinarily  to  be  in  a  great  measure  independent 
of  the  brain  ;  while  on  the  other  hand,  in  relation  to  voluntary 


164  HUMAN  PHYSIOLOGY. 

The  spinal  marrow  performs  two  separate  functions. 

motion  and  sensation,  it  forms  the  chain  of  communication  be- 
tween the  brain  and  the  moving  and  sentient  parts.  In  this 
respect  the  dependence  is  perfect.  In  injuries  of  the  spine, 
therefore,  the  extent  of  the  loss  of  the  power  of  motion  and  of 
sensibility  depends  on  the  nearness  of  the  injury  to  the  brain. 
The  higher  up  the  injury  is,  the  larger  is  the  number  of  nerves 
•whose  connection  with  the  brain  is  cut  off,  and  therefore  the 
greater  is  the  extent  of  body  rendered  insensible  and  motionless. 

258.  The  spinal  marrow  then  performs  two  separate  functions 
— one,  in  producing  involuntary  motion,  as  an  organ  by  itself; 
and  another,  as  an  organ  in  connection  with  the  brain,  in  the 
production  of  voluntary  motion  and  sensation.     The  arrange- 
ment, by  which  it  does  two  things  which  are  so  different  from 
each  other,  will  be  clear  to  you,  if  you  bear  in  mind  the  fact 
that  the  spinal  marrow,  like  the  brain,  is  composed  of  the  two 
nervous  substances,  the  white  tubular,  and  the  gray  vesicular  sub- 
stance.    When  the  spinal  marrow  acts  as  a  mere  medium  of 
communication  for  the  brain,  the  transmission  is  made  directly 
through  the  tubes  of  the  white  substance  to  and  from  the  brain 
— to  the  brain  in  sensation,  and  from  it  in  voluntary  motion. 
Thus,  when  a  sensation  is  felt  in  the  foot,  the  impression  made 
there  is  transmitted  through  the  nerve  to  the  spinal  marrow, 
and  up  through  the  white  part  of  this  organ  to  the  brain.     It 
touches  none  of  the  gray  substance  of  the  spinal  marrow,  but 
goes  to  the  gray  substance  of  the  brain.     And  when  the  foot  is 
moved,  an  impression  is  returned  from  the  brain  through  the 
white  part  of  the  spinal  marrow,  and  then  through  the  nerve 
which  goes  from  it  to  the  muscles  that  move  the  foot.     But,  on 
the  other  hand,  when  the  spinal  marrow  acts  by  itself,  inde- 
pendently of  the  brain,  producing  what  is  called  reflex  action, 
(§  255,)  the  impressions   that  are  transmitted,  some  of  them 
begin,   and  some  end    in  the  gray  substance  of   the    spinal 
marrow.     The  impression  on  an  excitor  nerve  ends  there,  and 
the  impression  on  a  motor  nerve  begins  there,  the  latter  result- 
ing from  the  former,  except  when  motion  is  produced  by  dis- 
ease in  the  spinal  marrow  itself.     Thus,  in  breathing,  as  de- 
scribed in  §  255,  an  impression  goes  from  the  lungs  through 
excitor  nerves  to  the  gray  substance,  and  that  is  the  end  of  it ; 
but  another  impression  begins  there  as  a  result  of  it,  and  is 
transmitted  to  the  involuntary  muscles  moving  the  chest. 

259.  One  marked  distinction  between  the  brain  and  spinal 
marrow  is,  that  the .  brain  has  its  intervals  of  rest ;  but  the 
functions  of  the  spinal  marrow  never  cease  for  a  moment  as 


THE  NERVOUS  SYSTEM.  165 

The  brain  rests.     The  spinal  marrow  does  not.     Convulsions. 

long  as  life  continues.  In  sleep  the  brain  is  more  or  less  at 
rest,  and  it  is  in  a  state  of  entire  torpor  when  the  sleep  is  pro- 
found. But  during  sleep  the  heart  beats,  the  respiratory- 
muscles  work  the  chest,  and  the  muscular  coat  of  the  stomach 
churns  the  food  if  there  be  any  there.  For  these  motions,  with 
many  others,  are  dependent  upon  the  spinal  marrow,  and  not 
upon  the  brain;  and  so,  while  the  brain  sleeps,  the  spinal 
marrow  keeps  up  the  operations  of  the  system  that  are  essential 
to  the  continuance  of  life,  in  the  manner  described  in  §  255. 
So,  also,  in  apoplexy,  when  the  brain  is  torpid  from  the 
pressure  of  blood,  the  spinal  marrow,  being  unaffected,  keeps  up 
the  functions  of  those  organs  which  are  dependent  upon  it. 
But  besides  the  motions  that  I  have  mentioned,  as  being  kept 
up  by  the  spinal  marrow,  when  the  brain  is  torpid  from  any 
cause,  there  are  other  motions  which  can  be  excited  by  stimu- 
lating nerves  that  are  connected  with  the  spine.  For  example, 
the  act  of  swallowing  can  be  produced  by  pouring  a  liquid  into 
the  mouth,  and  motion  can  be  produced  in  the  muscles  of  a 
limb  by  irritating  the  limb  at  different  points.  If  you  cut  off 
the  head  of  a  frog,  and  thus  destroy  all  sensibility,  you  can 
produce  movements  in  his  limbs  by  irritating  them.  You 
can,  indeed,  make  the  whole  body  to  move  together,  by 
producing  irritation  at  many  points  at  the  same  time.  So,  too, 
if  a  man  be  paralyzed  in  his  lower  limbs  by  a  blow  upon 
the  spinal  column,  these  parts,  which  he  cannot  move  by  his 
will,  can  be  excited  to  motion  by  irritation  with  electricity 
or  other  agents. 

260.  The  motions  of  the  muscles  in  convulsions  are  pro- 
duced by  the  agency  of  the  spinal  marrow.  The  irritation 
causing  them  sometimes  exists  in  the  spinal  marrow  itself, 
being  the  result  of  disease  there.  But  commonly  the  irritation 
is  in  some  other  part  of  the  system,  and  it  produces  the  con- 
vulsive movements  by  sending  an  impression  through  excitor 
nerves  to  the  spinal  marrow,  to  be  reflected  back  through  the 
motor  nerves,  as  described  in  §  255.  The  brain  during  the 
convulsion  is  in  a  torpid  state,  the  individual  being  uncon- 
scious. That  the  brain  is  involved  to  some  extent  in  the  con- 
vulsion is  very  clear,  and  sometimes  the  cause  of  the  convul- 
sion is  in  this  organ.  But  it  is  probable  that  the  convulsive 
movements  are  directly  dependent  on  the  spinal  marrow,  and 
that  even  when  the  cause  is  in  the  brain,  it  is  by  the  action  of 
the  spinal  marrow,  sympathizing  with  and  affected  by  the 
diseased  brain,  that  the  convulsion  is  produced.  And  when 


166  HUMAN   PHYSIOLOGY. 

Involuntary  action  of  voluntary  muscles.     How  produced. 

the  cause  is  in  some  other  part,  as  in  the  irritation  of  teething 
or  indigestion,  the  impression  is  sent  directly  to  the  spinal 
marrow,  and  is  reflected  from  it  to  the  muscles,  the  brain  being 
only  secondarily  affected. 

261.  It  is  worthy  of  remark,  that  in  convulsions  there  is  a 
purely  involuntary  action  of  muscles,  that  are  ordinarily  under 
the  control  of  the  will.     How  is  this  ?     How  are  they  taken 
away  from  the  usual  control  of  the  will  so  suddenly  and  so 
entirely  ?     It  is  not  possible  that  any  temporary  new  connec- 
tions can  be  established  all  at  once  by  the  disease, — that  there 
is,  to  use  illustrations  of  a  familiar  character,  a  sort  of  unship- 
ping of  the  usual  connection,  and  a  hitching  on  of  another  for 
the   time   being,   or  a   switching  off  from  one   track   on   to 
another.     These  voluntary  muscles  must  have  all  the  time  a 
connection  with  the  gray  substance  of  the  spinal  marrow,  just 
as  the  involuntary  muscles  have,  only  it  is  not  as  intimate  and 
extensive.     If  it  were  not  so,  they  could  not  act  occasionally  a9 
involuntary  muscles.     Being  thus  connected  with   the  gray 
substance,  both  in  the  brain  and  spinal  marrow,  when  they 
act  in  obedience  to  the  will,  the  impression  exciting  their  ac- 
tion  comes  to  them   from  the   gray  substance  in  the  brain 
through  the  white  part  of  the  spinal  marrow ;  but  when  they 
act   involuntarily,  the  impression  comes  from  the   gray  sub- 
stance in  the  spinal  marrow,  and  not  from  the  brain. 

262.  I  may  remark  farther,  that  the  voluntary  muscles  act 
involuntarily  more    often   than   is   commonly  supposed.     As 
already  stated,  (§259)  in  animals,  from  which  the  head  has 
been  removed,  the  voluntary  muscles  can  be  excited  to  involun- 
tary   action,   resembling   voluntary   movements,   although  of 
course  with  the  removal  of  the  head  were  destroyed  all  sensa- 
tion and  all  exercise  of  the  will.     And  in  the  case  of  the  man 
paralyzed  by  injury  in  the  back,  alluded  to  also  in  §  259,  in- 
voluntary movements  can  be  excited  in  the  voluntary  muscles. 
A  pigeon,  whose  cerebrum  had  been  removed,  would  fly  when 
thrown  into  the  air,  would  run  when  it  was  pushed,  and  would 
drink  when  its  beak  was  put  into  water.     There  was  no  sensi- 
bility and  no  will  in  this  case,  for  they  can  not  be  without  the 
cerebrum.     The   movements   were   involuntary,   though   per- 
formed by  voluntary  muscles.     Now  as  these  facts  prove  that 
voluntary  muscles  are,  through  their  connection  with  the  spinal 
marrow,  capable  of  acting   as  involuntary  muscles   also,  the 
question  arises,  whether  they  do  not  much  of  the  time  act  in 
part  as  involuntary  muscles,  and  sometimes  wholly  so.     That 


THE  NERVOUS   SYSTEM.  167 

Walking.     Reverie.     Brain  not  directly  essential  to  life. 

this  is  the  case,  a  little  reflection  will  show.  When  we  are 
walking  we  use  voluntary  muscles.  But  manifestly  a  distinct 
act  of  the  will  is  not  put  forth  for  every  motion  performed 
in  walking.  The  mind  may  be  at  the  same  time  fixed  upon 
something  else  ;  and  there  seems  ordinarily  to  be  only  an  oc- 
casional action  of  the  will,  as  when  we  change  our  course,  or 
when  some  obstacle  is  in  the  way,  requiring  a  variation  from 
the  regular  consecutive  series  of  movements.  There  is  a  dis- 
tinct action  of  the  will  when  the  movements  begin ;  but  after 
this  the  motions  seem  for  the  most  part  almost  automatic,  and 
are  probably  produced  by  the  reflex  action  of  the  spinal  mar- 
row, the  will  interfering  only  when  occasion  requires.  This  is 
more  manifestly  the  case  when  one  is  walking  in  a  reverie,  and 
perhaps  finds  himself  on  awaking  from  it,  in  a  different  place 
from  that  to  which  he  had  willed  to  go.  It  is  as  if  the  brain 
set  the  machinery  of  the  limbs  to  work,  and  then  delivered  it 
over  to  the  care  of  the  spinal  marrow,  interfering  only  when  it 
needs  to  do  so  to  meet  some  difficulty,  or  when  it  wishes  to 
give  a  new  direction  to  the  movement,  or  to  stop  it.  And  in 
a  reverie,  the  brain  occupied  with  other  things,  neglects  even 
to  exercise  this  superintendence,  and  leaves  the  machinery 
wholly  to  the  guidance  of  the  spinal  marrow.  The  same  re- 
marks can  be  made  in  regard  to  other  motions,  as  in  speaking, 
singing,  playing  on  an  instrument,  &c.  In  all  these  cases  the 
voluntary  muscles  act  in  some  measure  involuntarily,  being 
governed  by  an  association  in  their  action  which  is  far  from 
being  wholly  dependent  upon  the  brain,  and  the  direction  of 
the  will.  I  shall  recur  to  this  point  again,  when  I  come  to 
treat  of  the  connection  between  the  mind  and  the  body. 

263.  Many  experiments  have  been  tried  upon  animals  in 
reference  to  the  functions  of  the  brain,  and  of  the  spinal  mar- 
row. I  have  already  alluded  to  some  of  them.  It  was 
formerly  supposed,  that  the  brain  was  the  only  centre  of  nerv- 
ous power,  and  that  it  was  immediately  essential  to  the  pre- 
servation of  life.  But  these  experiments  have  shown  that  this 
is  far  from  being  the  truth.  The  brain,  it  has  been  found,  has 
nothing  to  do  directly  with  the  maintenance  of  life.  Animals 
live  for  some  time  after  the  brain  is  destroyed.  A  pigeon  was 
kept  alive  for  some  months  after  its  cerebrum  was  removed. 
Its  condition  was  very  much  like  that  of  a  man,  the  functions 
of  whose  cerebrum  are  suspended  by  the  pressure  of  a  frac- 
tured portion  of  the  skull.  Although,  like  him,  the  animal 
had  lost  all  sensation  and  voluntary  motion,  yet,  like  him,  it 


168  HUMAN  PHYSIOLOGY. 


Upper  part  of  the  spinal  cord  directly  essential  to  life. 


continued  to  breathe,  and  its  heart  continued  to  beat.  Of 
course  so  extensive  an  injury  of  so  important  an  organ  will  at 
length  cause  death  ;  but  life  continues  long  enough  in  such 
cases  to  show,  that  this  organ  is  not  immediately  essential  to 
its  continuance.  The  functions  most  essential  to  life,  the 
respiration  and  circulation,  are,  as  you  have  seen,  "kept  up  by 
the  spinal  marrow.  The  very  upper  part  of  this  organ  is  espe- 
cially devoted  to  this  purpose.  You  may  take  out  the  brain 
of  an  animal,  and  destroy  all  its  spinal  marrow,  except  this 
upper  portion  of  it,  and  the  animal  will  still  breathe,  and  its 
heart  will  beat.  But  if  you  destroy  just  this  small  portion  of 
the  spinal  marrow,  though  you  leave  the  rest  of  it  and  the 
brain  untouched,  the  animal  will  die  at  once  from  the  cessa- 
tion of  the  respiration  and  the  circulation.  In  the  Spanish 
bull-fight,  when  the  matadore  at  length  kills  the  animal,  by 
adroitly  piercing  the  spine  in  the  back  of  the  neck,  he  inflicts 
his  wound  upon  this  upper  part  of  the  spinal  marrow. 

264.  If  after  cutting  off  the  head  of  a  frog,  you  divide  the 
spinal  marrow  in  the  back,  you  can  produce  involuntary  mo- 
tions in  both  the  upper  and  lower  extremities.  But  you  can  not 
produce  them  at  the  same  time  in  both  together,  for  the  divi- 
sion of  the  spinal  marrow  in  the  back  separates  it  into  two 
independent  parts.  When,  therefore,  you  irritate  the  upper 
extremities,  the  motion  is  confined  to  them,  and  the  lower  ex- 
tremities are  quiescent.  And  if  you  irritate  the  lower  extrem- 
ities, the  motion  produced  there  does  not  extend  to  the  upper. 
The  division  can  be  carried  much  farther  with  similar  results. 
If  the  spinal  marrow  be  divided  above  and  below  where  a  pair 
of  nerves  is  given  off,  so  as  to  separate  this  point  wholly  from 
the  rest  of  the  nervous  system,  the  reflex  action  can  be  excited 
in  the  nerves  connected  with  this  point.  That  is,  an  irritation 
of  the  parts  supplied  by  the  excitor  nerve  of  this  little  segment 
of  the  spinal  marrow  will  produce  an  impression  in  that  seg- 
ment, which  will  be  reflected  by  the  motor  nerve  to  the 
muscles.  The  gray  substance  of  the  spinal  marrow  may,  there- 
fore, be  regarded  as  a  chain  of  little  brains,  in  some  measure 
separate  from  each  other.  But  while  there  are  thus  many 
centres  of  reflex  action,  there  is  only  one  centre  of  sensation 
and  voluntary  motion,  and  that  centre,  the  brain,  is  connected 
with  the  mind.  Some  physiologists  have  maintained  that 
there  is  sensation  independent  of  the  brain;  but  it  may  be 
considered  as  most  abundantly  proved,  that  it  is  through  the 
brain  alone  that  the  mind  feels  and  acts,  or  rather  that  we 


THE   NERVOUS   SYSTEM.  169 


Two  systems  of  nerves,  cereoro -spinal  and  sympathetic. 

know  nothing  in  this  world  of  a  sentient   and  acting  mind 
existing  without  a  brain. 

265.  The  system  of  nerves  which  we  have  been  examining 
is  termed  the  ccrebro-spinal,  from  its  two  great  central  organs, 
the  brain  and  spinal  marrow.  But  there  is  another  nervous 
system,  the  functions  of  which  are  involved  in  much  mystery. 
It  is  called  the  system  of  the  great  sympathetic,  or  the  sympa- 
thetic system.  Sometimes  it  is  called  the  nervous  system  of 
organic  life,  because  it  is  so  intimately  and  extensively  con- 
nected with  the  nutritive  processes  ;  while  the  system  that  we 
have  been  considering  is  called  the  nervous  system  of  animal 
life,  because  it  regulates  the  functions  peculiar  to  animals  in 
distinction  from  plants,  sensation,  and  spontaneous  motion. 
While  the  sympathetic  system  is  thus  connected  with  the 
nutritive  processes,  it  is  also  supposed  to  be  the  means  of  effect- 
ing the  sympathetic  connection  between  different  parts  of  the 
body,  and  to  act  as  the  medium  by  which  the  passions  and 
emotions  of  the  mind  produce  their  effects  upon  the  functions 
of  the  different  organs.  In  this  system  there  are  many  gang- 
lions or  little  brains,  which  communicate  with  each  other  by 
nerves.  There  is  a  chain  of  them  along  in  front  of  the  spinal 
column,  and  there  are  two  quite  large  ones  in  the  abdomen. 
This  system  has  connections  everywhere  with  the  cerebro-spinal. 
The  purposes  aimed  at  in  the  particular  arrangements  of  this 
system  are  as  yet  but  little  understood,  and  we  probably  never 
shall  know  as  much  about  it  as  we  shall  about  the  cerebro- 
spinal  system.  The  arrangement  of  the  sympathetic  system 
differs  very  materially  from  the  cerebro-spinal.  It  is  a  single 
system,  and  has  no  symmetrical  arrangement,  while  the 
cerebro-spinal  has  throughout  two  halves  which  are  precisely 
alike. 

I  have  thus  described  the  arrangements  and  functions  of  the 
nervous  system  to  such  an  extent,  as  will  prepare  you  for  the 
consideration  of  those  subordinate  organs,  by  which  the  pur- 
poses of  this  system  are  accomplished.  After  treating  of  the 
organs  of  locomotion,  the  voice,  and  the  senses,  I  shall  call  your 
attention  again  to  this  system,  presenting  some  views  of  its 
uses  and  connections,  which  you  will  then  be  better  prepared 
to  understand. 

15 


170  HUMAN  PHYSIOLOGY. 

Bones  the  framework  of  the  body.     Composition  of  bone. 


CHAPTER  XI 

THE  BONES. 

266.  THE  bones  furnish  the  points  of  support  and  attach- 
ment for  the  muscles  which  move  the  different  parts  of  the 
body.     They  are,  therefore,  the  passive  instruments  of  loco- 
motion.    I  treat  of  the  bones  before  the  muscles,  because  you 
will  then  better  understand  the  action  and  the  arrangement 
of  the  muscles. 

267.  The  bones,  forming  the  framework  of  the  body,  not 
only  furnish  points  of  support  and  attachment  to  the  muscles, 
but  in  many  cases  serve  to  defend  important  organs  from  in- 
jury.    Thus,  the  soft  brain  is  thoroughly  secured  from  harm 
by  being  inclosed  in  the  skull ;  and  the  lungs  are  surrounded 
by  walls  of  bone  so  arranged,  as  you  saw  in  the  chapter  on 
Respiration,  that,  while  they  defend  the  lungs  from  external 
violence,  they  secure  a  wide  range  of  motion  for  the  necessary 
expansion  of  these  organs. 

268.  The  bones  are  composed  of  two  parts,  the  earthy  or 
hard  portion,  and  the  animal  portion  which  is  soft.     Each  of 
these  portions,  as  was  stated  in  §  60,  can  be  obtained  separate 
from  the  other.     These  two  portions  of  bone  exist  in  different 
relative  proportions  in  the  different  periods  of  life.     In  the 
child  the   animal   portion   predominates,   while   the    mineral 
does   in  old   age.     It  is  a   wise  provision   in  regard  to  the 
child,  for  if  his  bones  were   as  brittle  as  those  of  old  age, 
or  even  as  those  of  middle  life,  they  would  be  often  broken 
in  the  falls  to  which  the  child  in  its  feebleness  and  carelessness 
is  subjected. 

269.  There  are  some  points  of  interest  in  relation  to  the 
structure  of  bone  and  its  growth.     I  stated  in  §  61  that  bone  is 
generally  formed  in  cartilage,  the  cartilage  being  formed  first  as 
a  mould  for  the  bone.     Bone  is  deposited  in  two  forms,  solid  and 
cellular.     In  the  flat  bones,  as  in  the  skull,  the  cellular  struc- 
ture lies  between  two  plates  of  solid  bone.     In  the  long  bones 
the  cellular  part  is  at  the  two  ends,  and  is  covered  with  a 
thin   plate  of  solid  bone,  while  the   shaft  is  a  hollow  tube 
vith   the    bone   very   much    condensed.      This   arrangement 


THE  BONES. 


171 


Structure  of  bone.    Long  bones  hollow.     Marrow. 


is    seen     in    Fig.    83,     representing 
the  thigh-bone  and  the  bone  of  the  FIG.  83. 

arm.  Certain  well  known  mechanical 
principles  are  observed  in  this  arrange- 
ment. The  bone  would  be  unneces- 
sarily heavy  if  it  were  solid  through- 
out. Lightness  in  a  moving  limb  is 
of  considerable  importance.  At  the 
same  time  strength  is  to  be  carefully 
provided  for  in  a  bone  which  is  to 
sustain  the  weight  of  the  body,  and 
to  which  the  large  muscles  of  the 
thigh  are  attached.  By  having  the 
bone  hollow,  both  of  these  objects, 
lightness  and  firmness,  are  secured. 
The  principles  involved  are  recognized 
by  the  architect  in  the  construction 
of  pillars,  and  we  see  them  exemplified 
in  the  hollow  stalks  of  plants.  The 
hollow  pillar  has  more  strength  than 
the  same  quantity  of  matter  would 
have  if  in  one  compact  mass ;  and 
the  stalk  which  supports  the  full  clus- 
ters of  grain,  would  break  under  its 
load  as  it  moves  back  and  forth  in 
the  wind,  if  it  were  solid  instead  of 
being  hollow.  But  the  round  cavity 
of  the  shaft  of  the  bone  does  not 
extend  to  the  ends.  These  are  ne- 
cessarily large,  in  order  to  present  broad  surfaces  for  articu- 
lation with  the  neighboring  bones ;  and  strength  and  light- 
ness are  secured  in  this  case  by  a  cellular  arrangement  of  the 
bony  matter,  the  outer  plate  of  solid  bone  being  comparatively 
thin.  There  is  obviously  more  firmness  in  the  resistance  to 
shocks  or  pressure,  secured  in  this  way,  than  there  would  be  if 
the  bony  matter  were  all  consolidated  into  a  shell  containing  a 
cavity. 

270.  The  round  canal  in  the  shaft  and  the  cellular  structure 
at  the  ends  are  filled  with  an  oily  substance  called  marrow. 
This,  like  all  other  fatty  substances,  is  contained  in  fat  cells,  as 
described  in  the  chapter  on  Cell-Life.  The  marrow  is  also 
present  in  the  cellular  structure  between  the  plates  of  the  flat 
bones.  The  cavities  and  the  cells  in  bones  have  branching 


172 


HUMAN  PHYSIOLOGY. 


Mode  of  nutrition  in  bones.     No  bloodvessels  in  their  solid  parts. 

about  in  them  bloodvessels,  which  are  branches  of  arteries  and 
veins  that  enter  the  body  of  the  bone  at  some  particular  points, 
in  the  long  ones  near  the  middle  of  the  shaft.  It  is  from  these 
bloodvessels,  together  with  those  that  come  from  the  mem- 
brane investing  the  bone,  called  periosteum,  that  the  bone  is 
nourished.  But,  although  an  artery  runs  through  the  body  of 
the  bone,  to  branch  out  upon  the  walls  of  its  cavity,  none  of  its 
branches  enter  the  very  substance  of  the  bone.  How  then  is 
the  bone  nourished,  that  is,  constructed  and  kept  in  repair? 
The  manner  in  which  the  material  for  this  purpose  is  carried 
to  every  point  of  the  solid  bone  has  been  developed  by  the  aid 
of  the  microscope,  and  I  will  describe  it  to  you.  If  we  cut 
across  the  solid  portion  of  a  bone,  and  examine  it  with  a 
microscope,  we  see  here  and  there  orifices  of  certain  minute 
canals  that  run  lengthwise  of  the  bone.  These  canals  are 
found  to  communicate  with  the  cavity  of  the  bone  and  receive 
therefore  blood,  or  some  of  the  constituents  of  the  blood,  from 
the  bloodvessels  which  are  situated  there.  These  orifices,  as 
seen  under  the  microscope,  are  represented  in  Fig.  84.  Around 
these  orifices  a  a,  you  see  little  dark  spots  arranged  in  rings, 
with  lines  running  to  them  from  the  orifices.  By  magnifying 
the  section  of  bone  still  more,  we  see  what  these  spots  and  lines 
are.  The  dark  spots  are  small  cavities,  and  the  lines  are 
minute  tubes  running  to  them.  In  Fig.  85  is  a  representation 
of  this  arrangement  as  seen  in  a  little  portion  of  the  section  of 
bone,  more  highly  magnified  than  it  is  in  Fig.  84.  The 

FIG.  84. 


SECTION    OF    BONK. 


THE  BONES.  173 


No  sensibility  in  bones.    Variety  of  shape. 


tubes  pass  out  from  the  canals  to  the  rows  of  cavities  which 
are  around  the  canals,  and  thus  a  circulation  is  kept  up  at 
every  point  of  the  solid  bone.  It  is  supposed  that  the  blood 
itself  does  not  circulate  in  these  little  channels  and  cavities 
in  the  solid  bone,  but  a  fluid  containing  the  constituents  of 
bone.  For  these  channels  are  too  small  even  to  admit  the 
cells  which  the  microscope  shows  us  as  swimming  in  the  blood. 
The  fluid  that  circulates  in  them  is  selected  from  the  blood, 
which  is  contained  in  the  bloodvessels  in  the  cavity  of  the 
bone,  and  in  the  periosteum  that  envelopes  it. 

271.  It  is  a  very  common  popular  notion,  that  the  bones  are 
endowed  with  great  sensibility,  and  especially  the  central  part, 
the  marrow.     The  surgeon  is  very  often  asked  if  the  sawing  of 
the  bone  in  amputation  is  not  very  painful,  and  if  when  the  saw 
reaches   the   marrow   it  does  not   produce   agony.     But  the 
'hones  have  in  their  healthy  state  no  perceptible  sensibility,  as 
I  have  before  stated,  and  the  sawing  of  the  bone  in  amputation 
occasions  no  suffering.     When,  however,  a  bone  becomes  in- 
flamed, severe  pain  is  one  of  the  symptoms.     And  it  is  well 
that  it  is  so ;  for  if  it  were  not,  disease  might  go  on  to  pro- 
duce disastrous  results  in  a  part  so  covered  up  by  others,  with- 
out any  warning  of  the  danger  of  the  case. 

272.  The  bones  are  of  every  variety  of  shape,  to  suit  the 
various  offices  which  they  are  to  fulfill.     You  will  see  this  to  be 
true,  as  you  cast  your  eye  over  the  skeleton  as  represented  in 
Fig.  86.     You  first  observe  the  somewhat  round  box  of  bones, 
which  contains   the   brain,   and   at  the  same  time  furnishes 
sockets  for  the  eyes,  extended  irregular  surfaces  for  the  appara- 
tus of  smelling,  and  for  that  of  the  taste,  a  place  for  the  organs 
of  hearing,  and  at  its  lower  part,  in  connection  with  the  lower 
jaw,  a  mill  for  grinding  the  food.     Then  you  observe  the  many 
bones  of  the  thorax  or  chest,  containing  and  protecting  the 
heart  and   the  lungs.     The  spinal  column,  k,  composed  of 
twenty-four  bones,  you  see  as  a  firm  but  movable  pillar,  ex- 
tending the  whole  length  of  the  body,  and  having  its  base 
firmly  planted   upon  that  stout  thick  bone,  the  sacrum,  which 
is  wedged  in  so  tightly  like  the  key-stone  of  an  arch,  between 
the  broad  spreading  bones  on  either  sida.     To  this  pillar  are 
strongly  fastened  the  walls  of  the  chest ;  and  from  the  chest 
thus  supported  by  the  spine  hang  the  lax  front  and  lateral 
walls  of  the  abdomen.     Then  below  you  see  the  pelvis,  as  it  is 
called, — a  set  of  large  bones  so  arranged  in  a  bowl-form,  as  to 
offer  a  broad  surface  of  support  to  the  contents  of  the  abdomen. 

15* 


174 


HUMAN  PHYSIOLOGY. 


The  bones  of  the  skeleton. 


FIG.  86. 


SKELETON. 


THE   BON*,S.  175 


Bones  of  the  cranium  and  the  face. 


The  bone  called  the  ilium,  m  and  I,  on  either  side,  with  its 
flaring  upper  surface,  is  especially  serviceable  in  this  way. 
The  pelvis  also  furnishes  a  socket  for  the  round  head  of  the 
thigh  bone  s,  and  points  of  attachment  for  the  large  muscles 
that  move  the  lower  extremity.  You  observe  the  large  bones 
of  the  thigh  and  leg,  intended  to  give  firmness  to  the  lower 
extremity,  and  the  lighter  bones  of  the  arm  and  forearm,  fitted 
for  extent  and  quickness  of  motion.  And  finally,  you  notice 
the  numerous  bones  of  which  the  hand  and  foot  are  made  up, 
giving  them  with  the  intervening  cartilaginous  coatings,  great 
elasticity,  and  vast  variety  of  motion,  especially  in  the  hand. 

273.  I  will   notice   with   some   particularity  some   of  the 
bones,  of  which  I  have  given  a  general  description,  as  they  are 
united  together  to  form  the  whole  skeleton.     I  can  not  notice 
them  all,  nor  dwell  upon  every  point  of  interest,  for  this  would 
require  much  more  space  than  I  can  devote  to  the  subject.     I 
shall,  therefore,  select  those  points  which  can  be  made  most 
clear  and  interesting. 

274.  I  first  call  your  attention  to  the  bones  of  the  head,  as 
you  see  them  in  Fig.  87.     There  are  twenty-two  bones  in  the 
whole  head.     Fourteen  of  these  belong  to  the  face,  while  eight 
belong  to  the  cranium,  that  is  that  part  of  the  skull  which  in- 
closes the  brain.     Of  these,  notice  particularly  the  large  bone 
in  front  called  the  frontal  bone,  a,  making  the  forehead,  and 
below  forming  the  upper  portion  of  the  orbits  of  the  eyes ; 
the  parietal  bone,  b,  the  upper  lateral  part  of  the  dome  of  the 

FIG.  87. 


BONES    OF    THE    HEAD. 


176  HUMAN  PHYSIOLOGY. 

Why  so  many  bones  in  the  skull.     The  two  tables,  and  the  sutures. 

skull ;  and  c  the  temporal  bone  on  which  the  parietal  bono 
rests.  There  is  a  large  bone  in  the  rear  forming  the  back  of 
the  cranium  as  the  frontal  bone  does  the  front.  There  are 
also  two  bones  in  the  base  of  the  cranium  which  are  out  of 
sight  in  this  view  of  the  skull.  You  may,  perhaps,  be  disposed 
to  inquire  why  this  box  for  holding  the  brain,  should  be  made 
of  so  many  bones.  One  reason  is,  that  the  enlargement  of  the 
skull  from  infancy  to  adult  age  is  effected  more  easily  and 
better  than  it  would  be  if  the  cranium  were  one  bone.  Another 
reason  is,  that  even  in  the  adult,  in  whom  these  bones  are  at 
length  so  tightly  united,  violence  is  less  apt  to  produce  injury, 
from  the  giving,  as  it  is  expressed,  of  the  bones  upon  each 
other,  than  it  would  be  if  one  bone  made  the  whole  structure. 
And  this  is  especially  true  of  the  child,  in  whom  the  bones  are 
very  imperfectly  united.  Hence  it  is  that  the  frequent  falls  of 
children  upon  their  heads  so  seldom  do  any  injury. 

275.  The  principal  bones  of  the  head  are  composed  of  two 
solid  plates,  while  the  bony  matter  between  these  plates  is  ar- 
ranged in  a  cellular  or  sponge-like  form.     The  outer  table  or 
plate  (for  both  of  these  terms  are  used  in  relation  to  it)  is 
rather  rough,  and  in  some  parts  has  ridges  for  the  attachment 
of  muscles.     But  the  inner  plate  is  very  smooth  on  account  of 
the  soft  delicate  organ  that  is  contained  in  the  cranium.     It  is 
so  brittle  that  it  has  been  called  the  vitreous  table,  from  its  re- 
semblance to  glass  in  this  respect.     The  modes  of  the  joining 
of  the  bones  differ  in   the  two  tables.     In  the  outer  table  the 
joining  is  by  a  minute  dovetailing,  called  a  suture.     Numerous 
little  projections  from  one  bone  fit  accurately  into  correspond- 
ing spaces  in  the  edge  of  the  other.     This  is  very  well  repre- 
sented in  Fig.  88,  in  which  you  see  the  sutures  on  the  top  of 
the  skull ;  b  being  the  suture  which  is  formed  between  the 
two  parietal  bones ;  a  a,  that  between  the  parietal  and  the 
frontal  bone  in  front ;  and  c  c,  that  between  the  parietal   and 
the  bone  which  forms  the  back  of  the  cranium.     A  better 
joining  for  bones  of  such  a  shape  as  these  have  can  not  be  con- 
ceived of.     But  the  inner  table  is  joined  differently.     It  is  so 
brittle  that  the  small  projections  of  the  dovetailing  mode  of 
joining  would   not  answer  here,  for  they  would  break  very 
easily.     The  joining   accordingly  is   in  this  case  by  smooth 
accurately  fitted  edges,  somewhat  beveled,  so  that  one  slightly 
overlaps  the  other. 

276.  The  upper  part  of  the  cranium  is  in  the  shape  of  a 
dome,  and  is  constructed  upon  the  same  principles  that  such 


THE   BONES.  177 


The  cranium  a  dome.    Contrivances  for  giving  it  strength. 


FIG.  88. 


SUTURES    IN    THE    SKULL. 

structures  are  in  regard  to  resistance  to  pressure  or  violence. 
Just  as  in  the  domes  that  are  built  by  man,  so  in  this  dome 
of  the  cranium,  great  strength  is  secured  around  the  lower 
part,  so  as  to  resist  outward  lateral  pressure.  In  the  dome 
of  St.  Paul's  there  is  a  double  iron  chain  around  its  base 
for  this  purpose,  of  course  concealed  from  view.  In  the  head 
of  man  the  dome  may  be  considered  as  composed  of  the 
frontal  bone  in  front,  the  parietal  bones  at  the  side,  and  the 
occipital  bone  in  the  rear.  In  front  you  see  the  base  of 
the  dome  strongly  fortified,  in  the  heavy  arches  that  form  the 
upper  part  of  the  sockets  of  the  eyes,  and  on  the  jutting  edges 
of  which  are  the  eyebrows.  In  the  rear  the  base  of  the  occi- 
pital bone  is  very  thick,  and  is  fortified  with  ridges  which 
furnish  attachment  to  the  large  muscles  in  the  back  of  the 
neck.  But  the  most  marked  and  interesting  contrivance  for  the 
strengthening  of  the  base  of  this  dome  is  at  the  side.  It  is  where 
the  parietal  bone  6,  as  seen  in  Fig.  87,  is  joined  by  the  temporal, 
c.  The  joining  here  is  not  by  suture,  for  that  would  afford  no 
resistance  to  lateral  pressure,  either  outward  or  inward.  To 
secure  this  object,  the  lower  bone,  the  temporal,  laps  over  the 
upper,  the  parietal,  with  a  beveled  edge.  It  abuts  upon  or 
against  it  It  has  the  relation  to  the  parietal  of  a  buttress  to 


178  HUMAN-  PSYSIOLOGY. 

Defenses  of  the  brain.     Many  and  efficient. 

an  arch.  You  can  readily  see  that  when  great  pressure  is 
made  on  the  top  of  the  head,  as  when  a  heavy  load  is  carried 
there,  there  must  be  a  tendency  to  outward  lateral  pressure  at 
the  base  of  the  dome  of  the  cranium,  and  that  this  is  effectually 
resisted  by  the  temporal  bones  acting  as  buttresses.  The  same 
thing  is  true,  also,  when  a  blow  is  inflicted  on  the  top  of  the 
head.  And  if  a  blow  be  received  at  the  side  of  the  head,  on 
the  temporal  bone,  it  is  evident  that  the  bones  will  not  be  so 
apt  to  be  fractured  and  pressed  inward  upon  the  brain,  as  they 
would  be,  if  they  were  united  by  suture. 

277.  You  are  now  prepared  to  see,  to  what  extent  the  brain 
is  guarded  against  the  effects  of  violence  inflicted  upon  the 
head.  These  effects  come  either  from  fracture  of  the  bones, 
or  from  concussion  without  fracture.  In  either  case  the  vibra- 
tion of  the  parts  concerned  is  the  cause  of  these  effects.  The 
guards  of  the  brain  defend  it  from  injury  by  lessening  or  dif- 
fusing this  vibration.  And  it  is  to  be  observed,  that  when 
vibration  passes  from  one  texture  to  another,  it  loses  some  of 
its  force  in  the  change.  No  two  substances  vibrate  just  alike  ; 
and  when  a  vibration  in  one  is  communicated  to  another,  it  is 
modified,  and  is  therefore  lessened.  Some  substances  modify 
and  lessen  vibrations  communicated  to  them  more  than  others 
do.  If  you  apply  these  principles  to  the  effects  of  violence  on 
the  head,  you  at  once  see  that  the  brain  would  be  much  more 
apt  to  receive  a  dangerous  shock  from  the  vibration  occasioned 
by  a  blow,  if  its  coverings  were  condensed  into  one  firm  and 
thick  layer  of  substance,  than  it  is  now.  So  also,  if  the  bones  of 
the  head  were  in  one  solid  layer,  instead  of  having  two  layers,  or 
plates,  with  the  spongy  structure  between,  and  the  integuments 
were  all  consolidated  into  one  thick  substance,  there  would  be 
much  more  liability  to  fracture  than  there  is  with  the  present 
arrangement.  Observe  now  how  many,  and  how  various  are 
the  textures,  through  which  the  vibration  of  a  blow  must  pass, 
before  it  reaches  the  brain.  Outside  of  the  bone  there  is  first 
the  hair ;  next  comes  the  skin ;  then  there  is  the  cellular  mem- 
brane containing  some  fat;  then  a  muscular  coat;  and  lastly, 
the  lining  membrane  over  the  surface  of  the  bone.  These 
various  textures  must  deaden  very  much  the  force  of  a  blow, 
and  especially  the  outer  cushion  of  hair,  and  those  inner 
cushions,  as  we  may  call  them,  of  fatty  cellular  membrane  and 
of  muscle.  Then,  when  the  vibration  reaches  the  bone,  it  is 
lessened  by  the  two  plates  with  the  intervening  cells,  and 
there  is  diffused  largely  among  the  many  bones  that  unite  with 


THE  BONES.  179 


Skull  especially  guarded  at  some  points. 


the  one  on  which  the  force  comes.  Then  as  the  shock  goes 
into  the  brain,  it  is  still  farther  lessened  by  the  membranes 
which  cover  that  organ.  These  greatly  diminish  the  vibration, 
precisely  as  a  coating  of  leather  on  the  inside  of  a  bell  would 
deaden  its  vibration  when  produced  by  a  blow  upon  the  out- 
side. With  all  these  provisions  the  result  is,  that  comparative- 
ly few  of  the  blows  received  by  the  head  do  harm.  The  skull 
may  be  considered  as  a  sort  of  helmet  for  the  brain,  its  effect- 
iveness as  a  defense  being  very  much  increased  by  its  cover- 
ings and  linings. 

278.  There  are  some  ^special  guards  at  particular  points  in 
the  cranium,  where  there   is   much  liability  to   exposure   to 
violence.     Thus,  as  the  lower  part  of  the  frontal  bone,  where 
the  eyebrows  are,  is  especially  exposed,  the  distance  from  the 
surface  to  the  brain  is  made  considerable  by  an  intervening 
chamber  in  the  bone,  called  the  frontal  sinus.     This  sinus, 
which  varies  much  in  size  in  different  individuals,  is  lined  with 
a  membrane,  and  communicates  with  the  nose.     You  can  see 
that  this  arrangement  is  a  great  protection  to  the  bone  at  that 
point.     The  outer  plate  could  be  broken,  while  the  inner  is  not 
injured.     But  the  protection  which  this  arrangement  affords, 
is  not  confined  to  that  single  point ;  it  serves  also  to  deaden 
the  vibration  of  a  blow  received  by  any  part  of  the  forehead, 
or  by  the  forehead  as  a  whole.     The  side  of  the  head,  too,  is 
peculiarly  exposed   to   blows.     And,   therefore,   the   skull  is 
peculiarly  guarded  at  this  point.     Beside  the  overlapping  of 
the  temporal  bone  upon  the  parietal,  to  which  I  have  before 
alluded,  the  parietal  bone  is  made  thicker  at  its  lower  part, 
where  it  is  most  liable  to  be  struck,  than  it  is  in  most  of  the 
other   parts   of  it.     Then,  too,  the   place   of  joining   of  the 
temporal  and  parietal  bones  is  covered  over  by  a  thick  muscle, 
the   contractions  of  which  you  can  feel  if  you   press   your 
fingers  upon  the  temple  while  moving  the  lower  jaw  as  in  eat- 
ing.    This  cushion  of  muscle  is  of  great  use  in  breaking  the 
force  of  a  blow  received  in  that  quarter.     Other  points  might 
be  specified  where  there  is  arrangement  for  special  protection, 
but,  those  to  which  I  have  alluded  will  suffice. 

279.  The  cranium  not  only  contains  and  protects  the  brain, 
but  it  at  the  same  time  serves  various  other  purposes,  and  pro- 
tects other  important  organs.     The  tender  and  delicate  eye  has 
there  a  bony  socket  with  jutting  prominences  all  around  it,  to 
guard  it  against  violence.     The  exceedingly  minute  and  com- 
plicated apparatus  of  the  hearing  is  also  carefully  protected  fry 


180  HUMAN  PHYSIOLOGY. 

Complicated  and  extensive  cavities  in  the  nose. 

the  skull,  and  the  most  important  part  of  it  is  furnished  with 
winding  and  intricate  apartments,  halls  of  audience,  in  that  part 
of  the  temporal  bone  which  is  so  hard,  that  it  is  called  the 
petrous  or  rock-like  bone.  To  the  bones  of  the  cranium  are 
attached  in  various  ways,  the  fourteen  bones  of  the  face.  All 
these,  with  the  exception  of  the  lower  jaw,  are  immovable. 
The  two  principal  of  them  are  the  upper  jaw  bone,  and  the 
cheek  bone.  The  former  makes  with  its  mate  of  the  other 
side  the  forward  portion  of  the  roof  of  the  mouth,  the  palate 
bones  making  its  rear  portion ;  and  it  furnishes  the  sockets  for 
the  teeth.  It  also  at  its  upper  part  nmkes  nearly  the  whole^of 
the  floor  of  the  orbit  of  the  eye.  Trie  cheek-bone  forms  the 
outer  lateral  part  of  the  socket  of  the  eye,  and  sending  back  a 
process  or  projection  to  unite  with  one  from  the  temporal  bone, 
c,  Fig.  87,  forms  the  zygoma  or  arch,  inside  of  which  the  tempo- 
ral muscle  passes  down  to  be  fastened  to  the  lower  jaw.  The 
bones  of  the  nose  make  quite  a  complicated  series  of  cavities, 
for  the  purpose  of  presenting,  in  the  mucous  membrane,  which 
lines  them,  a  large  surface,  over  which  the  nerve  of  smell  is 
expanded.  A  representation  of  these  cavities  is  given  in  Fig. 
89  ;  in  which  a  is  the  mouth ; 
6,  the  opening  into  the  nos- 
tril ;  c?,  a  part  of  the  base  of 
the  skull ;  c,  the  communica- 
tion of  the  nostril  with  the 
back  of  the  throat ;  e,  the  cur- 
tain of  the  palate ;  /,  the  front- 
al sinus  ;  m,  another  large  si- 
nus ;  ^,  i,  A,  spongy  bones  pro- 
jecting into  the  cavity  of  the 
nostril.  There  is  a  large  sinus, 
that  is  not  seen  in  this  figure, 
which  lies  over  the  teeth  in  e  a 

the  jaw-bone.     The  different         INNER  BONES  OF  THE  NOSE. 
sinuses  are  lined  with  the  mu- 
cous membrane  extending  into  them  from  the  nose.     These,  with 
the  spongy  bones  make  a  very  large  extent  of  surface  in  the 
cavities  devoted  to  the  sense  of  smell.     The  branches  of  the 
nerves  of  smell   enter  these   cavities,  to   be   distributed  over 
thin  walls,  through  many  small  openings  in  a  bone  in  the 
roof  of  the  nose,  giving  it  a  sieve-like  appearance. 

280.  The  lower  jaw  is  a  bone  shaped  something  like  ahorse 
shoe,  with  its  ends  turned  considerably  upward.     It  has  two 


THE  BONES. 


181 


Structure  of  teeth.    Three  different  kinds  of  texture. 


smooth  projecting  surfaces  which  articulate  with  two  corres- 
ponding shallow  cavities  in  the  temporal  bone.  Its  prominence 
at  the  lower  part  in  front,  the  chin,  is  peculiar  to  man,  there 
being  no  such  prominence  in  any  other  animal.  The  lower 
jaw  has  sockets  for  the  teeth,  and  it  is  so  constructed,  and  is 
so  arranged  with  muscles,  that  these  teeth  can  be  brought  to 
bear  against  the  teeth  of  the  upper  jaw  in  cutting  and  grind- 
ing motions. 

281.  The  teeth  are  very  nearly  like  the  bones  in  their 
structure,  but  they  differ  from  them  in  some  particulars  which 
it  will  be  interesting  to  notice.  Every  tooth  has  in  it  three  dis- 
tinct structures,  which  differ  in  hardness,  for  reasons  which  will 
appear  clear  to  you  as  I  proceed.  The  dentine  or  ivory  consti 
tutes  the  body  both  of  the  tooth  and  of  its  fangs.  In  the  body 
of  the  tooth  there  is  a  coating  of  that  very  hard  substance,  the 
enamel,  over  the  whole  surface  of  the  ivory.  This  is  thickest 
over  the  top  of  the  tooth,  and  grows  thinner  on  the  sides  till 
it  is  entirely  gone  where  the  gum  begins.  The  ivory  in  the 
fangs  has  a  coating  of  a  very  different  character,  called  the 
cementum.  It  is  not  hard  like  the  enamel.  This  arrangement 
is  represented  in  Fig.  90.  This  is  a  tooth  with  two  fangs  or 
roots;  1,  is  the  enamel;  3,  the  den- 
tine or  ivory :  2,  and  7,  the  cement- 
um ;  4,  an  unnatural  enlargement  of 
the  cementum,  making  an  excres- 
cence ;  5,  the  cavity  of  the  tooth 
supplied  with  bloodvessels  and  nerves 
which  come  through  the  channels 
that  you  see  running  up  the  middle 
of  each  fang.  This  cavity  is  analo- 
gous to  that  which  is  found  in  the 
shafts  of  the  long  bones  as  seen  in 
Fig.  83.  The  ivory  and  the  cement- 
um are  seen  b^the  microscope  to  be 
very  differentmextures.  The  ivory 
is  traversed  by  innumerable  branch- 
ing tubes  running  from  within  out- 
ward towards  the  cementum,  as 
represented  in  Fig.  91.  This  is  a 
section  of  a  small  portion  of  the 
dentine  anc1  cementum  in  the  fang  of  a  tooth,  very  much  mag- 
nified, a,  a,  btaiig  the  dentine,  and  c,  c,  the  cementum,  evidently 
a  different  structure.  The  structure  of  the  enamel  as  exhibited 
16 


FIG.  90. 


Vertical 
SECTION  OF  A  TOOTH. 


182 


HUMAN   PHYSIOLOGY. 


How  teeth  are  different  from  bones,  and  why. 


FIG.  91. 


by  the  microscope  is  represented  in  Fig.  66  and  67,  in  the 
chapter  on  Cell-Life.  I  have  been  thus  particular  in  the 
description  of  the  parts  of  a  tooth,  that  you  may  see  how 
compound  even  so  apparently  simple  a  part  of  the  body  is. 
The  three  different  structures  in  it  are  built  by  cells,  and  the 
cells  of  each  part  select  from  the  blood  such  constituents  as 
are  needed  for  their  purpose. 

282.  A  tooth  differs  from  a  common  bone  in  one  import- 
ant particular — when  once  formed  it  is  never  altered  in  its 
size.  A  bone  grows  with  the  growth  of  other  parts  of  the 
body ;  but  a  tooth,  when  it  first  protrudes  through  the  gum  is 
as  large  as  it  ever  will  be.  The  reason  of  this  is,  that  so 
hard  a  substance  as  enamel  can  not  be  made  changeable  as 
bone  is.  Its  hardness  is  inconsistent  with  any  thing  like  cir- 
culation in  it,  and  without  circulation  there  can  be  no  change. 
If  the  enamel  were  not  needed,  and  the  teeth  could  be  com- 
posed only  of  dentine,  they  could  grow  as  other  bones  do. 
And  if  they  could  grow,  one  set  of  teeth  might  be  made  to 
answer  the  purpose.  As  it  is,  the  second  set  ar.e  needed,  be- 
cause as  the  jaws  grow,  the  first  set  are  neither  ISrge  enough  in 
proportion  to  the  size  of  the  jaws,  nor  numerous  enough  to 
fill  up  the  whole  space.  If  the  first  set  were  to  be  the  only 
set,  when  the  jaws  became  of  their  full  size,  the  teeth  would  be 
altogether  too  small,  and  would  be  quite  separated  from  each 
other.  Twenty  small  teeth  (the  number  of  the  first  set)  in  the 
jaws  of  an  adult,  in  place  of  the  thirty-two  large  teeth  of  the 
second  set,  would  present  a  very  odd  appearance,  besides  being 
incapable  of  doing  the  service  required  of  them. 


THE  BONES.  188 


Hyoid  bone.     Patella.    Spinal  column.    Its  firmness  and  flexibility. 

Under  the  lower  jaw  is  a,  little  bone,  called  from  its  resem- 
blance to  the  Greek  letter  v,  the  hyoid  or  u-like  bone.  Its 
round  end  is  towards  the  root  of  the  tongue,  and  its  two  ends 
reach  backward  towards  the  spine.  The  larynx  is  suspended 
from  it  as  from  a  frame,  and  the  muscles  that  draw  up  thig 
bone,  draw  up  the  larynx  with  it.  It  is  one  of  the  few  bones 
in  the  body  that  are  not  directly  connected  with  any  other 
bone.  The  patella,  or  kneepan,  is  one  of  these  bones.  The 
four  little  bones  in  the  ear,  of  which  I  shall  speak  particularly 
when  I  come  to  treat  of  the  sense  of  hearing,  are  not  connected 
with  any  other  bone. 

283.  I  pass  now  to  the  bones  of  the  trunk  of  the  body.  I 
shall  speak  first  of  the  spinal  column,  or  the  backbone,  as  it  is 
called  in  common  language,  as  if  it  were  all  one  bone.  In 
some  respects  it  does  act  as  one  bone,  although  it  is  made  up 
of  twenty-four  distinct  bones.  It  is  the  great  pillar  of  the 
body.  As  such,  it  has  the  head  resting  on  its  top,  and  it  fur- 
nishes support  for  the  walls  of  the  chest,  and  for  the  muscles 
which  make  up  the  most  of  the  walls  of  the  abdomen.  To  it 
also  are  fastened,  as  you  have  seen  in  the  chapter  on  Digestion, 
the  mass  of  intestines  in  the  abdomen,  and  indeed  to  some  ex- 
tent all  the  viscera  both  of  the  abdomen  and  the  thorax.  Sus- 
taining, therefore,  as  it  does  so  much  weight  in  so  many  ways, 
it  stands  firmly  planted  on  its  great  pedestal,  the  strong  broad 
bone  of  the  pelvis,  the  sacrum.  And  this  pedestal  is  supported, 
as  I  have  before  said,  after  the  manner  of  a  keystone,  between 
the  lighter  spreading  bones  of  the  pelvis  on  either  side.  But 
while  the  spinal  column  acts  as  a  strong  and  firmly  supported 
pillar,  it  is  necessary  that  it  should  loe  flexible  for  the  different 
motions  of  the  body.  It  is  therefore  composed  of  twenty-four 
bones  called  the  vertebra,  so  that,  as  in  any  considerable  motion 
of  the  column  as  a  whole,  there  is  but  little  motion  between 
any  two  of  them,  the  motion  does  not  interfere  with  its  office  as 
a  firm  pillar.  It  is  most  free  in  its  uppermost  part,  the  neck  ; 
it  is  considerable  in  its  lower  part,  the  small  of  the  back ;  and  it 
is  least  of  all  in  that  part  to  which  the  ribs  are  joined.  You 
readily  see  the  reasons  for  this  difference  in  motion  in  different 
parts  of  the  column.  For  the  varied  motions  of  the  head  there 
is  need  of  a  free  movement  between  the  vertebrae.  Then  for  the 
twisting  and  turning  motions  of  the  body,  you  have  the  free 
movement  between  them  at  the  lower  part  of  the  column, 
which  is  easily  provided  for  there,  because  there  are  attached  to 
that  portion  of  it  nothing  but  parts  that  are  pliable.  It  is  not 


184  HUMAN   PHYSIOLOGY. 

Vertebrae.     Processes  for  locking  strongly  together. 

so  with  that  portion  of  it  that  forms  the  supporting  pillar  of  the 
framework  of  the  chest.  There  is  little  motion  here  between 
the  vertebrae,  because  the  joining  of  the  ribs  to  the  column 
forbids  it. 

But  besides  serving  as  a  firm  pillar,  and  as  a  flexible  chain, 
the  spinal  column  also  forms  a  canal  or  tube  in  which  the 
spinal  marrow,  one  of  the  most  delicate  and  important  organs 
in  the  body,  is  securely  lodged.  This  canal  extends  through  its 
whole  length,  and  from  the  spinal  marrow  included  in  it  there 
pass  out  the  nerves  to  go  to  all  parts  of  the  body. 

284.  Having  thus  presented  a  general  view  of  the  spinal 
column,  I  will  now  give  a  particular  description  of  the  form 
and  arrangements  of  the  bones  of  which  it  is  composed,  so  that 
you  may  understand  how  the  various  objects  of  this  wonderful 
structure  are  secured.  In  Fig.  92  you  see  a  representation  of 


A  SIDE  VIEW  OF  A  VERTEBRA. 


A  VERTEBRA. 


one  of  the  vertebrae ;  a,  being  the  body  of  the  bone ;  5,  the  hole 
which  forms  this  vertebra's  part  of  the  canal  for  the  spinal 
marrow ;  and  c,  the  spinous  process.  It  is  these  spinous  pro- 
cesses that  make  the  row  of  projecting  points  seen  down  the 
length  of  the  back.  There  are  six  other  processes,  only  four  of 
which  you  can  see  in  the  figure.  Four  of  these  processes  serve 
to  lock  the  vertebra  with  its  two  adjoining  ones  above  and 
below,  which  they  do  so  strongly,  that  there  can  be  no  disloca- 
tion of  them  without  a  fracture.  Fig.  93  gives  a  side  view  of 
a  vertebra.  Strong  ligaments  bind  these  bones  together,  and 
there  are  very  numerous  muscles  attached  to  the  processes,  so 


THE   BONES. 


185 


Spinal  column.     Canal  through  it.     Cartilages. 


that  this  jagged  column  of  bones  is  very  thoroughly  enveloped 
in  softer  substances. 

285.  In  Fig.  94.  you  see   the    whole  FIG. 94. 

spinal  column  with  the  sacrum  on  which 
it  stands.  It  is  laid  open  by  a  verti- 
cal section  dividing  it  into  two  halves,  so 
as  to  show  the  manner  in  which  the  bones 
form  the  tube  that  contains  the  spinal 
marrow.  The  darkly  shaded  strip  through 
the  length  of  the  figure  represents  this 
tube.  It  extends,  you  see,  down  beyond 
the  limits  of  the  column  itself  through  the 
sacrum.  It  is  bounded  in  front  by  the 
bodies  of  the  vertebrae  represented  as  sawn 
through  from  front  to  rear,  and  by  the 
spinous  processes  behind  also  sawn  in  the 
same  way.  In  this  canal  you  see  there 
is  a  row  of  little  openings,  arranged  just 
behind  the  bodies  of  the  vertebrae. 
Through  these  openings,  each  of  which 
is  between  two  of  the  vertebrae,  the  nerves 
go  out  from  the  spinal  marrow.  The  ar- 
rangement is  such,  that  the  nerves  are 
very  securely  guarded  against  the  hazard 
of  pressure  in  the  movements  of  the  verte- 
brae upon  each  other.  You  see  also  that 
there  are  spaces  between  the  bodies  of  all 
the  vertebrae.  These  are  filled  with  car- 
tilages, which  vary  in  thickness  in  differ- 
ent parts  of  the  column,  from  one  quarter 
even  to  three  quarters  of  an  inch,  being 
thickest  in  the  lower  part  of  the  back, 
where  the  backward  and  forward  motion  ~* 

of  the  vertebrae  upon  each  other  is  the         SPINAL  COLUMN. 
greatest.     Each   cartilage   is   firmly    fas- 
tened to  the  two  vertebrae,  between  which 
they  are  situated,  by  the  rough  surface  of  the  body  of  the  bono 
which  you  see  represented  in  Fig.  92.     This  arrangement  of 
cartilages  is  an  important  provision  for  the  motion  of  the  spinal 
column.     It  contributes  greatly  to  its  flexibility.     When  you 
stoop  forward,  all  of  the  cartilages  are  compressed,  and  when 
you  rise  up  they  return  to  their  usual  size  by  their  elasticity. 
And  besides  this,  they  serve   to   diminish  any  shock   which 


186  HUMAN  PHYSIOLOGY. 

Spinal  column  shaped  so  as  to  guard  against  shocks. 

iniglit  otherwise  be  transmitted  through  the  column  of  bones 
to  the  head  with  too  great  force.  There  is  another  guard 
against  the  injurious  transmission  of  shocks  to  the  brain,  in  the 
shape  of  the  spinal  column,  the  twenty-four  bones  being  ar- 
ranged, not  in  a  straight  line,  but  in  a  double  curve.  The 
vibration,  communicated  upward  through  the  spinal  column,  is 
thus  not  only  lessened  by  the  elasticity  of  the  cartilages,  but  is 
also  distributed  in  different  directions  by  the  curved  arrange- 
ment of  the  bones.  If  the  column  had  been  made  straight, 
the  head  would  have  been  subject  to  frequent  jars  in  the 
movements  of  the  body,  which  would  be  disagreeable  and 
often  injurious. 

286.  You  have  thus  seen  how  three  different  objects,  ap- 
parently incompatible  with  each  other,  are  accomplished  in  the 
arrangement  of  the  spinal  column.     To  put  twenty -four  bones 
together  in  such  a  way,  that  they  shall  form  a  strong  firm 
pillar  for  the  whole  frame,  and  yet  they  shall  make  a  column 
or  chain  flexible  enough  for  the  various  motions  of  the  trunk 
of  the  body,  and  at  the  same  time  provide  in  this  column  a  se- 
cure canal  for  the  rod  of  nervous  matter  which  moves  all  the 
muscles  of  the  body,  is  to  produce  a  piece  of  mechanism  which 
far  transcends  any  thing  that  has  ever  been  contrived  by  the 
ingenuity  of  man. 

287.  There  remains  to  be  noticed  one  especial  contrivance 
in  the  spinal  column.     It  is  at  its  summit,  and  it  is  for  the 
purpose  of  providing  for  the  free  motions  of  the  head  in  various 
directions,  and  at  the  same  time  securing  the  spinal  marrow  at 
that   part  from   all  hazard  of  pressure  from   these   motions. 
These  two  objects  are  accomplished  in  this  way.     The  head  in 
moving  backward  and  forward  rocks  on  two  smooth  surfaces  on 
the  first  vertebra.     But  when  the  head  moves  to  the  right  and 
left,  this  first  vertebra  moves  along  with  the  head  on  the  second 
vertebra.     And  there  is  a  tooth-like  process  that  projects  up 
from  the  second  vertebra  inside  of  the  first,  around  which  this 
rotary  motion  is  performed.     In  Fig.  95  is  represented  the  first 
vertebra.     J.  J.  are  the  two  surfaces  on  which  the  head  rests, 
and  rocks  backward  and  forward.     A  is  the  opening  for  the 
spinal  marrow.     L  is  the  strong  ligament  which  confines  the 
tooth-like  process  that  projects  upward  from  the  second  verte- 
bra.    In  Fig.  96  is  the  second  vertebra.     P  is  the  tooth-like 
process,  around  which  the  first  vertebra  rotates,  carrying  the 
skull  with  it.     You  see  it  is  smaller  at  its  root  than  at  its  top. 
This  smaller  part  is  bound  firmly  by  the  ligament  in  the  first 


THE  BONES. 


187 


Arrangement  of  first  and  second  vertebras. 


vertebra.  It  is  shaped  thus  to  prevent  its  slipping  out  from  the 
ligament.  J,  J,  are  the  two  surfaces  on  which  the  first  verte- 
bra moves  as  it  rotates  around  the  tooth-like  process.  Fig.  97 
shows  the  two  bones  together,  the  tooth-like  process  being  con- 
fined in  the  ring  of  the  upper  bone.  Special  painsaretaken  to 
make  this  arrangement  secure,  that  the  process  may  not  be 
in  danger  of  pressing  upon  the  spinal  marrow  at  this  important 
point.  It  is  thus  that  the  lateral  rotary  motion  of  the  head  and 
the  forward  and  backward  motion  are  secured  by  two  joints, 
just  as  is  done  in  the  mounting  of  a  telescope.  The  difference 
between  the  two  cases  is,  that  in  the  mounting  of  the  telescope 
there  are  no  difficulties  to  overcome,  while  in  arranging  the 

FIG.  95. 


FIRST  VERTEBRA. 


FIG.  96. 


FIG.  97. 


First  and  Second 
VERTEBRAE  TOGETHER. 


SECOND  VERTEBRA. 


188  HUMAN  PHYSIOLOGY. 

Snecial  defense  of  spinal  cord  in  neck  of  birds. 

mounting  of  the  head,  as  we  may  term  it,  a  peculiar  contrivance 
and  a  nice  adjustment  are  needed  to  prevent  injury  of  a  very 
important  organ.  It  is  a  wonderful  contrivance,  by  which  so 
much  and  so  varied  motion  can  be  effected  in  the  very  walls  that 
contain  the  soft  and  delicate  spinal  marrow,  without  injuring 
it.  You  will  fully  appreciate  this,  if  you  observe  the  extent  and 
variety  of  the  motions  of  the  head  and  neck,  executed  chiefly 
with  the  two  bones  that  I  have  described. 

288.  In  the  neck  of  birds  there  is  a  contrivance  of  a  different 
character,  for  the  arrangement  which  answers  for  the  motions 
required  by  man,  obviously  could  not  secure  the  very  free  mo- 
tions which  the  bird  executes  with  its  neck.     As  the  bird  bends 
its  neck  at  such  abrupt  angles  in  all  directions,  a  peculiar  ar- 
rangement of  the  vertebrae  is  necessary,  to  prevent  the  spinal 
marrow  from  being  pressed  upon.     The  arrangement  is  a  sim- 
ple, but  effectual  one.     I  can  make  this  plain 

to  you  by  the  rough  diagram  in  Fig.  98.  A,  A, 
are  two  of  the  vertebrae  of  the  neck  laid  open. 
B  is  the  spinal  canal,  and  C  is  the  spinal  mar- 
row. You  observe  that  each  vertebra  is  larger 
at  its  ends  than  in  the  middle,  allowing  at  the 
joinings  of  the  bones,  where  the  motion  is,  a 
considerable  space  between  the  bone  and  the 
spinal  cord.  Now  if  each  of  these  bones  were 
of  equal  size  throughout,  and  the  spinal  mar- 
row filled  up  the  canal,  you  can  readily  see 
that  when  any  two  of  these  were  much  bent  SPINAL  COLUMN 
upon  each  other,  there  would  be  pressure  upon 
the  spinal  cord ;  and  pressure  would  produce  palsy,  and  often 
destroy  life.  But  with  the  simple  arrangement  above  described, 
free  motion,  almost  to  a  right-angle  in  some  directions,  can  be 
executed  without  pressing  on  the  cord.  And  besides  this,  you 
can  see  that  the  cord  by  this  arrangement  will  not  be  bent  at 
an  angle,  as  the  vertebrae  are,  but  in  a  curve,  for  the  spaces  in 
the  spinal  canal  at  the  joinings  allow  of  a  lateral  movement  of 
the  spinal  marrow  at  these  points. 

289.  It  would  be  interesting  to  consider  in  full  the  variations 
in  the  spinal  column  in  different  classes  of  animals.     But  I  will 
only  allude  to  a  few  of  them.     In  quadrupeds,  as  they  have 
their  heads  suspended,  instead  of  being  supported,  as  in  man, 
upon  a  column  of  bones,  the  spinous  processes  in  the  neck  are 
very  large,  and  project  much,  for  the  attachment  of  strong 
muscles  which  hold  up  the  head  and  move  it.     There  is  also 


THE  BONES. 


189 


Spinal  column  in  fishes,  reptiles,  and  in  neck  of  giraffe. 


FIG.  99. 


attached  to  these  processes,  a  very  stout  fibrous  ligament,  com- 
monly  called  the  paxy-waxy,  to  assist  in  sustaining-  the  head. 
In  fishes  the  spinal  column  is  so  arranged  as  to 
give  it  a  great  flexibility.     In  Fig.  99  is  repre- 
sented one  of  the  vertebrae  of  a  fish.     If  you 
compare  it  with  a  human  vertebra,  as  seen  in 
Fig.  92,  you  will  see  that  it  differs  very  widely 
from  it.     It  has  no  transverse  or  side  processes. 
While  the  human  vertebra  has  one  spinous  pro- 
cess that  projects  behind,  this  has  two  /,/,  one 
in  front  and  one  in  the  rear,  or  rather,  according 
to  the  usual  position  of  the  fish,  one  above  and 
one  below.     The  body  of  the  vertebra  has  a  cup- 
like  cavity  on  each  side  towards  its  neighboring 
vertebra.     When,  therefore,  two  of  these  vertebrae 
are  joined  together,  their  two  cup-like  cavities  make 
one  cavity  of  the  shape  of  a  double  cone,  as  seen  in  Fig.  100. 
This  is  a  representation  of  a  section 
of  a  portion  of  the  spine  of  a  fish. 
The  division  is  made  so  as  to  cut 
the  vertebrae  into  two  halves,  and 
thus   show   these   cavities.     Each 
one  of  these  contains  a  sac  which 
is  filled  with   a  gelatinous   fluid. 


FIG.  100. 


This  arrangement,  Avhich  secures 
very  great  flexibility  of  the  spinal 
column,  you  can  examine  at  any 
time  when  you  have  fish  on  the 
table.  The  long  spinous  processes 
make  the  broad  frame-work  of  the  SPINAL  COLUMN  OF  A  FISH. 
animal,  to  which  its  muscles  are 

attached.  In  reptiles  there  is  still  greater  flexibility  of  the 
spine  than  in  fishes.  This  is  secured  in  two  ways,  by  the 
great  number  of  the  vertebrae,  and  by  a  peculiar  arrangement 
of  them.  There  are  three  hundred  and  four  vertebrae  in  the 
boa  constrictor,  over  three  hundred  in  the  common  ringed 
snake,  and  over  two  hundred  in  the  rattle-snake.  The  articu- 
lations of  the  vertebrae  in  reptiles  are  with  a  ball  and  socket 
arrangement.  The  forward  part  of  each  vertebra  has  a  deep 
cup-like  depression,  in  which  plays  a  round  smooth  ball  from 
the  back  part  of  the  next  vertebra.  And  as  these  joints  are 
firmly  bound  together  by  ligaments,  the  spinal  column  is  very 
strong  as  well  as  flexible.  In  the  gracefully  flexible  neck  of  the 


190  HUMAN  PHYSIOLOGY. 

Arrangement  of  collar-bone,  shoulder-blade,  and  breastbone. 

giraffe  we  have  the  same  ball  and  socket  articulations  of  the 
vertebrae. 

290.  The  framework  of  the  chest  I  have  already  described 
sufficiently  in   the  chapter  on  Respiration.     The    breastbone, 
which  is  flat  and  of  simple  form  in  man,  is  much  larger  and 
less  simple  in  its  form  in  some  animals.     In  birds  it  is  not  only 
broader,  but  it  has  a  keel-shaped  projection  for  the  attachment 
of  the  large  muscles  used  in  flight.     The  clavicle,  g,  Fig.  86  (so 
called  from  its  resemblance  to  a  key,)  and  commonly  called 
the  collar-bone,  is  attached  at  one  end  to  the  top  of  the  breast- 
bone, and  at  the  other  unites  with  a  process  of  the  scapula,  or 
shoulder-blade  at  the  top  of  the  shoulder  joint.     It  is  a  prop  to 
the  shoulder,  pressing  it  outward  ;  and  accordingly  it  is  large  in 
those  animals,  the  movements   of  whose   superior  extremities 
tend  to  bring  the  shoulders  towards  each  other,  while  it  is  very 
slender,  or  absent  even,  in  those  the  tendency  of  whose  move- 
ments  is   to   keep  the  shoulders   apart.     Thus   in   birds   the 
drawing  down  of  the  wings  by  the  strong  muscles  would  bring 
the  shoulders  towards  each  other,  were  this  not  prevented  by 
stout  clavicles.     Sometimes  a  second  bone  is  added  for   the 
same  purpose.     But  in  the  horse  and  other  similar  animals,  the 
pressure  of  the  body  downwards  between  the  shoulders  tends 
to  separate  them,  and  here  we  find  the  clavicle  deficient  because 
it  is  not  needed.     The  scapula,  or  shoulder  blade  is  a  thin  bone 
with  a  stout  raised  spine  or  ridge  running  across  it,  and  ending 
in  forming  the  top  of  the  shoulder  joint.     It  is  situated  differ- 
ently from  any  other  bone  in  the  body.     It  is  imbedded  in 
muscles  and  has  a  very  free  motion.     Its  design  is  to  give  free- 
dom of  motion  to  the  arm.     It  is  directly  connected  with  the 
skeleton  only  by  its  union  with  the  clavicle.     In  Fig.  101  you 
see  the  arrangement  of  the  clavicle,  scapula,  and  breastbone. 
C,  C,  are  the  scapulae  or  shoulder-blades.     A,  is  the  upper  part 
of  the   breastbone.     B,  B,  are  the  clavicles  fastened  to   the 
breastbone  at  one  end,  and  to  the  shoulder-blade  at  the  other 
end  at  E,  which  is  a  process  of  the  shoulder-blade,  making  the 
projecting  top  of  the  shoulder-joint.     D,  is  another  process  of 
the  shoulder  which  serves  for  the  attachment  of  muscles  and 
ligaments.     It  is  called  the  coracoid  process,  from  its  resem- 
blance to  the  beak  of  a  crow. 

291.  The  upper  extremity  is  divided  into  three  parts,  the 
arm,  the  forearm,  and  the  hand.     The  arm  has  but  one  long 
bone,  the  humerus,  i,  Fig.  86.     This  has  a  round  head  which 
moves  in  a  shallow  cup  formed  bv  the  shoulder-blade.     The 


THE  BONES. 


191 


Collar-bones.     Shoulder-blades.    Bones  of  the  forearm. 


FIG.  101. 


THE    COLLAR-BONES    AND    THE    SHOULDER-BLADES. 

FIG.  102. 


192  HUMAN   PHYSIOLOGY. 

Arrangement  of  the  bones  of  the  forearm  for  rotary  motion.     Bones  of  the  hand. 

shallowness  of  the  socket  is  the  cause  of  the  frequent  disloca- 
tion of  the  shoulder.  But  if  there  were  a  deep  socket  like  that 
in  which  the  head  of  the  thigh-bone  is,  the  arm  could  not  have 
any  thing  like  the  freeness  of  motion  that  it  now  has.  Such  an 
arrangement  would  involve  too  much  of  a  sacrifice  of  necessary 
uses  for  the  sake  of  security.  At  its  lower  part  the  humerus 
makes  a  hinge  joint  with  the  forearm.  The  forearm  has 
two  bones,  the  radius,  b,  Fig.  102,  and  the  ulna,  a.  The  par- 
ticular arrangement  of  these  two  bones  is  worthy  of  notice. 
The  hinge-like  motion  of  the  forearm  upon  the  arm  is  per- 
formed by  the  ulna  alone.  This  bone  has  a  beak-like  process, 
which  works  over  a  smooth  round  surface  at  the  end  of  the 
humerus.  It  is  the  outside  of  this  process  which  you  feel  at 
the  point  of  the  elbow.  The  other  bone,  the  radius,  has 
nothing  to  do  with  this  motion.  This  only  rolls  on  the  ulna 
in  the  rotary  motions  of  the  forearm.  But  at  the  other  end  of 
these  bones,  at  the  wrist,  the  arrangement  is  reversed.  Here,  it 
is  the  radius  on  which  the  hand  moves  in  a  hinge-like  manner, 
while  the  ulna  at  c  rolls  on  the  radius,  as  the  radius  does  on  the 
ulna  at  the  elbow.  You  can  readily  see  that  as  the  radius  rolls 
on  the  ulna  at  the  elbow,  and  the  ulna  on  the  radius  at  the  wrist, 
a  very  free  rotary  motion  of  the  forearm  is  provided  for.  The 
combination  of  this  motion  with  the  motions  at  the  wrist,  the  el- 
bow, and  the  shoulder,  secures  that  almost  endless  variety  of  move- 
ment, which  is  so  striking  a  peculiarity  of  the  upper  extremity, 
as  compared  with  the  lower.  The  hand  is  divided  into  three 
parts,  the  carpus,  p,  Fig.  86,  composed  of  eight  smaif  bones, 
the  metacarpus,  q,  composed  of  bones  which  are  like  the  bones 
of  the  fingers,  r.  The  eight  bones  of  the  carpus  are  firmly 
packed  together,  but  they  have  a  slight  motion  upon  each 
other,  and  this,  together  with  the  motion  of  the  metarcarpal 
bones,  makes  the  hand  a  more  easy,  light,  and  springy  instru- 
ment than  it  would  be,  if  these  bones  were  all  consolidated  into 
one.  The  metacarpal  bones  are  the  framework  of  the  flat  part 
of  the  hand,  and  to  them  are  joined  the  first  row  of  the  bones 
of  the  fingers.  The  metacarpal  bone  of  the  thumb  has  a  very 
free  motion  upon  the  carpus,  differing  in  this  respect  altogether 
from  the  metacarpal  bones  in  the  body  of  the  hand.  The 
bones  in  the  wrist  and  hand  are  bound  together  by  very  strong 
ligaments.  Those  which  are  seen  in  the  palm  of  the  hand  are 
represented  in  Fig.  103.  Those  which  you  see  at  a,  b,  and  c 
bind  the  small  bones  of  the  wrist  together,  and  also  tie  them 
strongly  to  the  bones  of  the  forearm,  the  ends  of  which  you  see 


THE  BONES. 


193 


Ligaments  of  the  wrist  and  the  hand. 


FIG.  103. 


in  the  Figure.  The  bone  at  6,  to  which  so  many  of  these  liga- 
ments are  attached,  is  the  prominent  bone  which  you  feel  at  the 
beginning  of  the  palm  of  the  hand  on  the  side  towards  the 
body.  The  ligament  g  connects  this  bone  with  the  metacarpal 
bone  of  the  little  finger.  At  c?,  df,  are  ligaments  which  running 
across  the  hand  bind  the  metacarpal  bones  together  at  their 
beginning.  At  e,  e,  are  similar  ligaments  where  the  bones  of 
the  fingers  join  them.  The  bones  of  the  fingers  and  thumb  are 
strongly  held  together  by  lateral  ligaments,  as  seen  at  /,/. 
The  various  ligaments  of  the  wrist  and  hand  permit  a  slight 
motion  between  the  bones ;  and  thus  the  hand  has  freedom 
and  ease  in  its  motions  while  it  is  also  a  very  strong  and  firm 
instrument. 

292.  The  lower  extremities  have  some  resemblance  to  the 
upper  in  their  structure  and  arrangement,  but  they  differ  from 
them  in  some  important  respects.  Here  firmness  is  the  chief 
object,  while  freedom  of  motion  is  the  great  thing  to  be  secured 
in  the  structure  of  the  upper  extremities.  The  lower  extremi- 

17 


194 


HUMAN  PHYSIOLOGY. 


Bones  of  the  leg  and  the  foot.     Arranged  for  firmness. 


ties  are  chiefly  for  locomotion,  but  the  upper  are  fitted  for  a 
variety  of  purposes.  The  body  is  supported  upon  the  lower 
extremities,  and,  therefore,  the  thigh- 
bones have  sockets  in  the  broad  flar-  FIG>  104> 
ing  bones  of  the  pelvis  m  and  /,  Fig.  86. 
In  Fig.  104  is  represented  a  rear  view  of 
the  thigh-bone.  Its  head,  a,  is  round, 
and  fits  into  a  deep  socket  in  the 
pelvis.  At  b  is  a  depression  in  which 
one  end  of  a  stout  short  ligament  is 
fastened,  its  other  end  being  attached 
to  the  bottom  of  the  socket.  At  c  is 
the  neck  of  the  bone;  at  d  and  e  are 
two  projections  to  which  are  attached 
large  muscles  to  move  the  limb. 
Along  the  shaft  of  the  bone,  #,  there 
is  a  rough  ridge,  A,  to  which  muscles 
are  fastened ;  i  and  k  are  two  smooth 
surfaces  for  articulation  with  the  leg 
below.  At  t,  Fig.  86  is  the  bone 
called  the  patella  or  kneepan,  which 
answers  as  a  defense  to  the  joint, 
and  at  the  same  time  affords  a 
mechanical  advantage  to  the  muscles 
which  throw  the  leg  forward.  These 
muscles  are  fastened  to  the  upper 
part  of  the  patella,  and  then  a  con- 
nection is  formed  by  a  strong  tendon 
between  its  lower  part  and  the  large 
bone  of  the  leg.  You  see  at  once 
that  the  leg  can  be  thrown  forward 
with  more,  force  by  this  arrangement, 
than  it  could  be  if  the  tendon  of  the 
muscles  passed  over  the  front  of  the 
joint  without  any  patella.  I  shall 

refer  to  this  again  in  the  Chapter  on  the  Muscles.  The  leg, 
like  the  forearm,  has  two  bones,  v  and  u,  Fig.  86  ;  but  unlike 
them  they  are  constructed  and  arranged  for  strength,  and  not 
for  freedom  of  motion.  The  foot,  like  the  hand,  is  divided  into 
three  parts.  The  tarsus,  a,  Fig.  105,  is  that  part  of  the  foot 
which  extends  from  the  heel  to  the  middle  of  the  foot.  It  is 
composed  of  seven  bones,  the  largest  of  which  makes  the  body 
of  the  heel.  The  metatarsus,  p?  has  .five  long  bones  reaching 


THE  BONES. 


195 


Elasticity  of  the  foot.     Arrangement  for  oiling  the  joints. 


FIG.  105. 


from  the  tarsus  to  the  toes.  The  toes,  c,  have  fourteen  bones* 
The  object  of  having  so  many  bones  in  the  body  of  the  foot  is 
to  give  a  certain  springiness  to  it,  which  guards  against  shocks, 
and  facilitates  motion.  Its  arched  form  also  tends  to  secure  the 
same  object.  In  every  movement  of  the  foot  there  is  a  slight 
motion  between  all  these  bones.  Thus  in  walking,  when  the  foot 
first  touches  the  ground,  it  does  so  at  the  heel,  as  represented  in 
Fig.  105.  Then  as  the  body  moves  forward,  the  fore-part  of  the 
foot  is  brought  down,  the  weight  of  the  body  at  length  press- 
ing upon  the  ground  at  the  ball  of  the  foot,  b.  In  executing 
this  movement,  elasticity  is  given  to  the  tread  of  the  foot  by 
the  very  slight  motion  which  occurs  between  these  many 
bones.  If  the  body  of  the  foot  were  all  one  'bone  it  would 
manifestly  be  a  very  stiff  and  awkward  affair,  and  ease  and 
grace  in  walking  would  be  an  impossibility.  With  such  a  foot 
we  should  not  walk  much  better  than  one  does  with  a  wooden 
leg. 

293.  Before  leaving  the  subject  of  the 
bones,  I  will  call  your  attention  to  the 
provision  which  is  made  for  the  easy 
movement  of  their  joints.  The  ends  of 
the  bones  are  tipped  with  cartilage,  so  as 
to  afford  a  firm  but  smooth  surface  for  the 
motion  of  the  one  bone  upon  the  other. 
Besides  this  provision,  the  ends  of  every 
two  bones  that  move  upon  each  other  are 
lined  with  a  membrane,  so  arranged  as  to 
make  a  blind  sac.  This  is  illustrated  in 
Fig.  106,  in  which  a  and  b  are  the  ends 
of  two  bones,  the  sac,  c,  lying  between 
them  represented  here  as  detached  from 
the  bone,  in  order  that  the  arrangement  DIAGRAM 

maybe  clear  to  you.     It  is  as  if  a  small       .bowing  Aiming  of  »j 


FIG.  106. 


196  HUMAN  PHYSIOLOGY. 

Each  fibril  of  a  muscle  supplied  by  a  nervous  tubulus. 

bladder  were  introduced  between  the  two  ends  of  the  bones, 
and  were  fastened  all  over  the  surfaces  that  press  together. 
The  inside  of  this  sac  is  kept  lubricated  with  a  bland  fluid  re- 
sembling the  white  of  egg,  so  that  the  joint  may  work  easily. 
This  fluid  is  secreted  by  the  membrane  itself,  and  the  moving 
machinery  of  the  human  system  may  therefore  be  said  to  oil 
its  own  joints.  In  the  knee-joint,  the  broad  surfaces  of  which 
are  subjected  to  so  much  pressure,  there  are  two  flat  pieces  of 
cartilage  loose  in  the  joint,  which  operate  like  friction  wheels  in 
lessening  the  friction.  There  is  a  similar  provision  in  the 
articulation  of  the  lower  jaw.  This  member  does  so  much 
work  in  talking,  and  such  heavy  work  in  mastication,  that  each 
of  its  joints  has  a  movable  cartilage  for  the  diminution  of 
friction.  Sometimes  when  the  lubricating  fluid  is  deficient,  or 
becomes  too  thick,  a  disagreeable  crackling  noise  is  produced 
by  these  cartilages  in  the  motions  of  the  jaw. 


CHAPTER  XII. 

THE  MUSCLES. 

294.  HAVING  described  the  bones,  I  now  proceed  to  speak 
of  the  muscles,  which  move  them  and  other  parts  of  the  frame. 
I  have  already  described  the  structure  of  muscles  in  §  203  in 
the  chapter  on  Cell-Life.  Each  fibril,  you  there  saw,  is  a  chain 
of  cells,  and  it  is  the  shortening  of  all  these  chains  of  cells  in  a 
muscle  that  produces  its  contraction.  The  action  of  a  muscle 
is  dependent  upon  the  nerves.  Each  fibril  has  a  nervous  fibril 
or  tubulus,  (§  232.)  by  which  its  connection  with  the  brain  or 
spinal  marrow  is  established.  And  each  fibril  is  in  this  respect 
probably  wholly  separate  from  every  other  fibril.  When,  there- 
fore, the  mind  wills  that  a  certain  motion  shall  be  performed, 
an  impression  (§  232)  is  sent  to  each  fibril  of  every  muscle  en- 
gaged in  that  motion,  through  the  tubulus  devoted  to  that 
fibril.  When  the  action  is  a  very  compound  one,  calling  into 
operation  many  muscles,  a  multitude  of  these  impressions  are 
communicated  through  a  multitude  of  distinct  channels  or 
tubuli.  The  individual  is  not  at  all  conscious  of  the  compound 
nature  of  muscular  action,  and  he  knows  nothing  of  the  muscles 


THE   MUSCLES.  197 


Relation  of  muscles  and  tendons.    Their  relative  size. 


which  produce  any  particular  movement,  unless  he  has  studied 
anatomy  and  physiology.  He  wills  the  movement  to  take 
place,  and  at  once  the  requisite  impressions  are  sent  along  the 
appropriate  channels  or  tubuli  to  their  destination.  These  im- 
pressions must  differ  in  degree  or  intensity  in  producing  differ- 
ent amounts  of  motion  ;  and  they  must  differ  in  some  cases  in 
different  parts  of  the  same  muscle,  as  some  fibres  are  put  in 
motion  while  others  are  not,  or  as  some  act  with  more  force 
than  others.  I  will  not  dwell  here  on  this  point,  as  I  shall 
recur  to  it  in  another  part  of  this  chapter,  when  I  come  to 
speak  of  the  compound  character,  and  the  varieties  of  motion. 

295.  Muscles  commonly  end  in  tendons,  which,  as  they  are 
white  and  shining,  are  quite  in  contrast  with  the  red  muscular 
fibres.     The  tendons  have  in  themselves  no  power  of  contrac- 
tion, but  are  mere  passive  cords.     They  have  the  same  relation 
to  the  muscles,  that  ropes  have  to  the  men  that  pull  them. 
They  are  of  various  shapes,  according  to  circumstances.     Long 
and  slender  tendons  may  be  seen  on  the  back  of  the  hand  in 
thin  persons,  the  muscles  that  pull  them  being  in  the  full  arm 
above.     The  tendons  are  not  bounded  by  a  distinct  line  where 
they  join  the  muscles,  but  tendinous  and  muscular  fibres  inter- 
twine, so  that  they  appear  to  run  insensibly  into  each  other. 
Tendinous  fibres  also  mingle  in  the  same  way  with  the  fibres  of 
bone,  making  so  strong  an  union,  that  a  great  force  exerted  in 
pulling  on  the  tendon  will  sooner  effect  a  rupture  of  the  tendon 
or  the  bone,  than  a  separation  of  the  connection  between  them. 
The  tendons  are  very  strong,  being  made  of  very  condensed 
fibrous  substance.     The  tendon  of  a  muscle  is,  therefore,  much 
smaller  than  the  muscle  itself.     This  is  a  circumstance  of  much 
importance  in  the  arrangement  of  the  moving  apparatus  of  our 
frames.     The  bulky  muscles  and  the  slender  tendons,  are  so 
arranged,  for  example,  in  the  limbs,  as  to  give  them  both  free- 
dom of  motion  and  beauty  of  form.     The  muscles  that  move 
the  fingers  help  to  make  up  the  full  part  of  the  arm,  while 
their  slender  tendons  occupy  but  little  space  as  they  play  over 
the  bones  of  the  wrist.     If  there  were  no  tendons,  and  the 
muscles  were  extended  to  the  parts  which  they  move,  the  hand 
would  be  a  large  cumbrous  mass,  instead  of  the  light  and  agile 
thing  that  it  is  now.     For  the  muscles  would  of  necessity  be 
continued  of  their  full  size,  and,  therefore,  the  bones  would  of 
course  be  very  large  in  order  to  afford  an  attachment  to  the 
muscles. 

296.  In  the  action  of  the  muscles  upon  the  bones,  we  havo 

17* 


198 


HUMAN   PHYSIOLOGY. 


The  three  kinds  of  lever  exemplified  in  the  action  of  muscles. 

examples  of  the  three  kinds  of  levers  treated  of  in  natural  phi- 
losophy. Some  of  these  I  will  now  notice.  The  first  kind  of 
lever  has  the  fulcrum  between  the  weight  and  the  power,  as 
represented  in  Fig.  107.  F  is  the  fulcrum,  W  the  weight,  and 

FIG.  107. 


FIRST  KIND  OF  LEVER. 

P  the  power.  You  have  examples  of  this  lever  in  the  common 
pump  handle,  the  beam  of  a  pair  of  scales,  the  crowbar,  as 
commonly  used,  scissors,  <fec.  You  have  an  example  of  this  form 
of  lever  in  the  human  body,  in  the  action  of  the  muscles  in 
moving  the  head  back  and  forth  on  the  top  of  the  spinal 
column.  In  this  case,  when  the  head  is  moved  forward,  the 
top  of  the  spine  is  the  fulcrum,  the  weight  to  be  moved  is  the 
back  of  the  head,  and  the  power  is  the  contraction  of  the  muscles 
that  bow  the  head  forward.  When  the  head  is  bent  backward, 
the  power  is  the  contraction  of  the  muscles  behind4,  and  the 
weight  is  the  front  part  of  the  head.  The  muscles  that  move 
the  head  backward  are  stronger  than  those  that  move  it  for- 
ward. It  is  necessary  that  it  should  be  so,  for  there  is  more  of 
the  head  in  front  of  the  point  of  support  or  fulcrum  than  there 
is  behind  it.  Hence,  when  sleep  relaxes  the  muscles,  if  we  are 
sitting  up  the  head  falls  forward. 

297.  In  the  second  kind  of  lever  the  weight  is  between  the 
fulcrum  and  the  power,  as  represented  in  Fig.  108.  The  com- 
mon wheelbarrow  is  an  example  of  this  form  of  lever.  You 
have  an  example  of  it  in  the  body  in  the  raising  of  the  heel 

FIG.  108. 


SECOND  KIND  OF  LEVER. 


THE   MUSCLES. 


199 


Motion  of  the  foot  in  walking. 


from  the  ground  in  walking.  In  doing  this  the  weight  to  be 
raised  is  the  whole  body,  the  foot  being  the  lever,  and  the 
forward  part  of  the  foot  being  the  fulcrum.  This  will  be  made 
slear  by  Fig.  109.  W  is  the  large  bone  of  the  leg  sustaining 


FIG.  109. 


the  weight  of  the  body ;  F,  is  the  fulcrum,  the  forward  part  of  the 
foot  that  presses  on  the  ground  as  the  heel  is  raised ;  and  P,  is 
the  large  muscle  in  the  calf  of  the  leg,  the  power  that  raises 
kthe  heel,  the  end  of  the  lever. 

298.  In  the  third  form  of  lever  the  power  is  between  the 
weight  and  the  fulcrum.  A  common  example  of  this  is  seen 
in  the  raising  of  a  ladder.  The  fixed  foot  of  the  ladder  is  the 
fulcrum,  the  ladder  itself  is  the  weight,  and  the  power  is  ap- 
plied as  far  from  the  fulcrum  as  it  can  be.  Fig.  110,  represents 

FIG.  no. 


THIRD    KIND    OF    LEVER. 


a  lever  of  this  kind.  This  form  of  lever  is  more  frequently 
used  than  the  other  forms  in  the  human  body.  We  have  an 
example  of  it  in  bending  the  forearm  upon  the  arm  as  seen  in 
Fig.  Ill,  in  which  1  is  the  bone  of  the  arm;  2,  the  tones  of 
the  forearm  ;  4,  the  muscle  which  bends  the  forearm  upon  the 
arm ;  5,  its  double  headed  attachment  above ;  and  6,  its  at- 


200  HUMAN  PHYSIOLOGY. 


Tw,  objects  aimed  at  in  muscular  action  ;  quickness  and  power. 


no.  111. 


tachm-mt  to  the  radius,  one  of  the  bones  of  the  forearm.  In  this 
case  the  fulcrum  is  at  8,  the  joint  of  the  elbow,  the  weight  is 
the  hand  with  whatever  it  holds,  and  the  power  is  applied  at 
the  point  where  the  tendon  is  fastened  to  the  ulna,  that  is,  as  in 
the  case  of  the  ladder,  between  the  fulcrum  and  the  weight. 
The  muscle  which  straightens  the  forearm  upon  the  arm  is 
represented  at  7.  I  shall  remark  upon  this  in  another  con- 
nection. 

299.  In  the  management  of  the  three  kinds  of  levers  there, 
are  two  different  objects  aimed  at  under  different  circumstances. 
One  object  is  to  move  a  great  weight  with  a  small  power. 
Here  quietness*  is  not  aimed  at,  but  the  weight  is  moved  slowly. 
The  other  object  is  to  move  the  weight  quickly,  an  object  in- 
consistent with  the  moving  of  any  very  heavy  weight.  When 
the  object  is  to  move  a  heavy  weight  slowly,  the  lever  is  so 
managed  as  to  get  a  good  purchase,  as  it  is  expressed.  Thus 
in  the  case  of  the  lever  of  the  second  kind,  Fig.  108,  if  the 
weight  be  a  heavy  one,  the  power  is  commonly  applied  at  some 
distance  from  the  weight.  The  nearer  the  power  is  to  the 
weight,  the  greater  must  it  be  to  move  the  weight.  The  smaller 
the  power,  the  further  must  it  be  from  the  weight  in  order  to 
raise  it.  But  though  a  small  power  if  at  a  distance  from 
the  weight  answers  to  raise  it,  yet  in  this  case  the  power  must 
move  through  a  considerable  space  to  move  the  weight  but 
little  ;  while  to  raise  the  weight  to  the  same  height,  a  power 
nearer  to  it  passes  through  but  little  space.  This  will  be  made 
clear  to  you  by  Fig.  112.  F  is  the  fulcrum,  and  W  the  weight. 
If  the  lever,  A,  be  raised  to  the  line,  B,  the  dotted  lines  will 
show  the  different  spaces  which  the  power  passes  through,  ac- 
cording to  its  distance  from  the  weight.  If  the  power  be  at  P, 


THE   MUSCLES.  201 


Quickness  more  often  important  thun  power. 


FIG.  112. 


A 


it  passes  through  the  space  indicated  by  the  dotted  line  a  in 
moving  the  weight  W  to  c.  But  if  it  be  at  p,  it  passes  through 
a  much  shorter  space,  6,  in  raising  the  weight  to  the  same 
height.  The  more  important,  therefore,  in  this  form  of  lever 
quickness  of  movement  is,  the  nearer  to  the  weight  is  the 
power  applied.  Let  us  look  at  the  application  of  these  prin- 
ciples to  the  example  of  this  kind  of  lever,  which  I  cited  from 
the  human  body,  represented  in  Fig.  109,  the  raising  of  the 
weight  of  the  body  on  the  foot  in  walking.  The  power  is  here 
applied  quite  near  to  the  weight,  for  quickness  in  raising  the 
heel  in  walking  and  running  is  of  great  importance.  By  hav- 
ing the  heel  project  farther  behind,  the  muscle  could  be  at- 
tached farther  from  the  weight,  and  thus  act  with  more  power. 
But  there  would  in  this  case  be  a  sacrifice  of  quickness  of  move- 
ment, and  besides  this,  the  lengthened  heel  would  present  a 
very  awkward  and  ugly  appearance. 

300.  But  it  is  in  examples  of  levers  of  the  third  kind  that 
we  find  these  principles  best  illustrated.  This  form  of  lever  is 
much  more  often  used  in  the  mechanism  of  the  muscles  than 
the  other  forms.  I  refer  you  to  the  example  given  of  this  lever 
in  the  action  of  the  biceps  muscle  in  bending  the  forearm,  as 
shown  in  Fig.  111.  In  this  case  it  is  of  much  more  importance 
to  move  small  weights  quickly,  than  to  move  heavy  ones  slowly. 
Therefore  the  power  is  applied  quite  near  to  the  fulcrum.  The 
tendon  of  the  biceps,  as  you  see,  is  fastened  to  the  main  bone 
of  the  forearm  near  the  fulcrum,  the  elbow.  You  can  readily 
see  that  the  point  where  the  power  is  applied  would  pass 
through  but  a  little  space,  in  moving  a  weight  through  a  con- 
siderable one.  The  lower  jaw,  in  its  upward  motion,  is  a  lever 
of  the  same  kind.  In  this  case,  force  rather  than  quickness  is 
required  in  breaking  and  grinding  the  food.  Here,  therefore, 
the  power,  the  action  of  the  muscle,  is  applied  farther  from 
the  fulcrum  than  in  the  case  of  the  biceps  muscle  of  the  arm, 


202 


HUMAN  PHYSIOLOGY. 


Force  most  important  in  the  case  of  the  lower  jaw. 


and  nearer  to  the  weight  to  be  moved,  or  the  point  where  the 
resistance  is  which  is  to  be  overcome.  It  is  applied  also  in  a 
different  direction,  a  point  which  I  shall  however  speak  of  in 
another  connection.  The  muscles  which  move  the  lower  jaw 
upward  can  be  seen  in  Fig.  113.  One  is  the  large  spreading 

FIG.  113. 


MUSCLES  OF  FACE  AND  NECK. 

muscle  &,  the  swelling  of  which,  in  its  contraction,  we  can  feel, 
if  we  place  the  fingers  on  the  temple  while  moving  the  lower 
jaw  upward.  The  other  is  the  short  strong  muscle  c,  the  front 
edge  of  which  is  so  far  forward,  that  one-third  at  least  of  the 
lower  jaw-bone  is  embraced  by  this  muscle.  Now,  if  you  com- 
pare this  bone  as  a  lever  with  the  forearm  as  acted  upon  by 
the  biceps,  you  will  at  once  see  that  the  power  is  applied  much 
nearer  to  the  weight,  or  the  resistance  to  be  overcome,  in  the 
case  of  the  jaw,  than  in  the  case  of  the  arm.  It  is  so  even  when 
the  resistance  to  be  overcome  is  at  the  front  teeth ;  and  it  is 
much  more  so  when  the  resistance  is  at  the  back  part  of  the 
mouth,  as  when  we  are  grinding  our  food.  Here,  indeed,  a  por- 
tion of  the  muscular  force  is  brought  to  bear  upon  the  resistance 
in  a  direct  line.  It  is  not  merely  because  the  back  teeth  aro 


THE   MUSCLES.  203 


Mechanical  disadvantage  in  muscular  action. 


stronger  than  the  front  ones,  but  also  because  the  power  is  nearer 
the  resistance,  that  we  can  crack  a  nut  more  easily  with  the 
back,  than  we  can  with  the  front  teeth. 

301.  It  is  clear  that  the  biceps  muscle  acts,  as  it  is  expressed, 
at  a  mechanical  disadvantage,  if  we  regard  mere  power  or  force, 
and  leave  out  of  view  quickness  of  motion.  If  it  were  inserted 
further  down  on  the  forearm,  nearer  the  hand,  it  could  raise 
much  greater  weights  than  it  now  can.  And  the  same  can  be 
said  of  most  of  the  other  muscles  of  the  body.  But  force  is 
sacrificed  for  the  sake  of  quickness  in  most  cases,  because  the 
latter  is  more  important.  In  the  few  cases  in  which  force  is 
more  important,  as  in  the  case  of  the  lower  jaw  just  cited,  the 
reverse  arrangement  is  provided.  The  gain  in  quickness  in  the 
arrangement  of  the  biceps  muscle  can  be  illustrated  on  Fig.  114. 

FIG.  114. 


/\     P  P 

F  being  the  fulcrum,  the  power  in  raising  the  weight,  W,  to  c, 
if  acting  at  P,  passes  through  the  space  indicated  by  the  dotted 
line  a.  But  if  it  act  at  jo,  it  will  pass  through  all  the  space  6, 
and  of  course  raise  the  weight  more  slowly  than  when  acting  at  P. 
302.  Most  of  the  muscles  work  at  a  mechanical  disadvantage 
in  another  way.  I  refer  to  the  direction  in  which  the  muscle 
acts  on  the  bone  to  be  moved.  This  is  seldom  at  right  angles, 
and  therefore  a  considerable  part  of  the  force  exerted  is  lost. 
This  can  be  made  clear  to  you  by  Fig.  115.  Let  b  represent 
the  bone  of  the  arm,  and  r  its  fulcrum,  or  point  of  support  in 
the  shoulder.  You  readily  see  that  if  the  bone  be  acted  on  by 
a  muscle,  ra,  at  right-angles  to  it,  it  will  require  less  force  to 
move  it  to  a  given  point  than  would  be  required  if  the  same 
muscle  were  placed  in  the  position  represented  by  n.  For  the 


204:  HUMAN"   PHYSIOLOGY. 

When  loss  in  power,  gain  in  quickness. 


FIG.  115. 


muscle  W,  acting  obliquely  on  the  bone  would  expend  a  part  of 
its  force  in  pressing  the  end  of  the  bone  upward  against  the 
socket  of  the  joint  at  r. 

303.  But  in  this  case  also,  what  is  lost  in  power  is  gained  in 
quickness  of  movement.     This  can  be  shown  on  the  figure. 
We  will  suppose  that  the  muscle  contracts  or  shortens  itself  the 
half  of  the  length  of  the  teuton.     If  the  muscle  were  placed  as 
at  ra,  the  bone  would  be  earned  to  the  line  «,  c.     But  if  the 
muscle  be  placed  as  at  n,  the  same  degree  of  contraction  would 
raise  the  bone  to  the  line  a,  rf,  the  point  of  the  bone  where  the 
tendon  of  the  muscle  is  attached  moving  in  the  curved  line  as 
marked.     The  resistance  to  be  overcome,  of  course,  requires 
much  more  power  for  the  obliquely  placed  muscle,  n,  to  raise 
the  bone  to  the  line  a,  rf,  than  for  the  muscle  m  to  raise  it  to 
a,  c  ;  and  therefore  a  much  larger  muscle  is  needed  than  there 
would  be  if  it  acted  at  right-angles  to  the  bone  as  at  m.     And 
the  muscle  which  raises  the  arm  at  the  shoulder,  acting  as  it 
does  at  so  great  disadvantage,  is  a  very  large  muscle.     The 
muscle,  w,  in  the  figure  represents  only  the  line  of  its  action, 
and  not  at  all  its  shape.     If  you  observe  the  various  motions  of 
the  arm  in  which  this  muscle  has  a  part,  you  will  appreciate 
the  necessity  of  so  arranging  it  as  to  secure  quickness  of  move- 
ment.    This  was  the  chief  object  to  be  aimed  at  in  its  arrange- 
ment; and   the  second  and   less   important  object,  power,  is 
secured,  so  far  as  it  is  needed,  by  simply  making  the  muscle  a 
large  one. 

304.  The  mechanical  disadvantage,  which  I  have  noticed  as 
resulting  from  the  oblique  action  of  the  muscles,  is  in  part  ob- 
viated by  a  very  simple  contrivance.     It  is  done  by  making  the 


THE  MUSCLES. 


205 


Contrivance  to  change  the  direction  of  force. 


FIG.  116. 


i J 


FIG.  117. 


-—o 


tendon  of  the  muscle  work  over  an  enlargement  of  the  bones  at 
the  joints.  The  operation  of  this  contrivance  can 
be  made  clear  by  Figs.  116  and  117.  Let  r  and 
o  (Fig.  116)  be  the  two  bones  of  a  joint,  and  let 
the  muscle  m  be  attached  to  the  bone  o  at  i.  As 
it  contracts,  almost  all  its  force  will  be  spent  in 
drawing  the  bone  o  upward  against  the  bone  r, 
because  it  acts  almost  entirely  in  a  line  with  the 
bones.  But  let  the  ends  of  the  bones  be  en- 
larged as  in  Fig.  117,  and  you  can  see  that  the 
direction  of  the  tendon  of  the  muscle  m  is  so 
changed  where  it  is  attached  to  the  bone,  that  the 
muscle  can  now  very  easily  make  the  lower  bone 
turn  upon  the  upper.  The  enlargement  then  of 
the  bones  at  the  joints,  which  is  needed  to  give 
the  requisite  extent  of  surface  for  working  them, 
answers  also  another  good  purpose  in  thus  alter- 
ing the  direction  of  force  in  the  muscles.  In  the 
case  of  the  knee-joint  there  is  an  additional  contrivance  for 
making  this  change  of  direction  still  greater.  A  movable  bone, 
the  patella  or  kneepan,  besides  acting  as  a  protection  to  the 
joint,  effects  also  the  purpose  referred  to.  The  manner  in  which 
it  does  this  can  be  made  plain  by  Fig.  118,  in  which  a  represents 
the  end  of  the  thigh-bone  ;  6,  the  end 
of  the  large  bone  of  the  leg  articulat- 
ing with  it ;  c,  the  patella  ;  rf,  the  large 
tendon  which  comes  from  the  muscle 
above,  and  is  fixed  into  the  patella ; 
and  e,  the  tendon  which  goes  from 
the  patella  to  the  large  bone  of  the 
leg  below.  The  dotted  line  shows 
how  much  the  direction  of  the  force 
of  the  muscle  is  changed  by  this  ar- 
rangement. The  movement  performed 
by  this  muscle  is  throwing  the  leg  and 
foot  forward,  which  it  is  by  the  above 
arrangement  of  the  patella  enabled  to 
do  with  great  ease  in  walking,  and 
with  great  force  in  the  act  of  kicking. 
305.  The  pulley  is  used  in  the  ar- 
rangement of  the  muscles,  though  by 
no  means  as  often  as  the  lever.  It 

serves,  whenever  it  is  used,  to  give  the  force  a  different  direction 

18 


FIG.  118. 


206  HUMAN  PHYSIOLOGY. 

The  pulley-arrangement  in  muscles. 

from  what  it  would  otherwise  have.  I  will  cite  but  a  few 
examples.  At  the  wrist  and  the  ankle  there  are  broad  liga- 
ments, which  bind  down  the  tendons  of  the  muscles,  and  sus- 
tain to  them  the  relation  of  pullies.  If  it  were  not  for  these 
ligaments  the  tendons  at  these  joints  would  fly  out  continually 
when  the  muscles  are  in  action,  making  projecting  cords  under 
the  skin.  And  if  the  skin  were  removed,  the  tendons  would 
be  in  a  position  similar  to  that  represented  at  A,  in  Fig.  119. 

FIG.  119. 


In  this  Figure,  C  is  the  tendon  of  the  great  toe  in  its  position  as 
bound  down  by  ligaments.  Now  if  the  muscle  were  in  the 
position  represented  by  A,  it  is  plain  that  it  would  act  at  a 
greater  mechanical  advantage  than  in  the  position  C ;  but  the 
toe  would  not  be  moved  as  quickly ;  and  besides,  if  the  tendons 
projected  in  this  way,  the  foot  would  be  a  very  cumbrous  piece 
of  machinery,  compared  with  what  it  is  now,  with  the  tendons 
bound  down  around  the  slender  ankle.  So  that  both  beauty 
and  use  are  secured  by  the  arrangement. 

306.  There  is  a  beautiful  application  of  the  pulley  in  the 
case  of  the  muscle  that  draws  down  the  lower  jaw,  called 
the  digastric  muscle.  It  is  represented  in  Fig.  120,  in  which 
a  is  one  end  of  the  muscle  attached  behind  the  ear,  and  b  is  the 
other  end  attached  to  the  inside  of  the  lower  part  of  the  chin. 


THE  MUSCLES.  207 


Manner  in  which  the  lower  jaw  is  drawn  down. 


FIG.  120. 


DIGASTRIC    MUSCLE. 

It  is  muscular  at  the  two  ends,  and  tendinous  in  its  middle 
part.  This  middle  part  runs  through  a  loop  or  ring  in  a  small 
muscle  as  represented  in  the  Figure.  This  little  muscle  is 
fastened  above  to  a  small  process  of  bone  under  the  ear,  and 
below  to  the  hyoid,  or  U-shaped  bone,  c,  which  is  situated  just 
above  the  larynx.  Now  when  the  jaw  is  to  be  drawn  down, 
the  two  fleshy  ends  of  the  digastric  muscle  contract,  and  the 
middle  tendinous  part  works  in  the  ring  provided  in  the  little 
muscle.  This  muscle  is  so  slender,  that  its  loop  is  of  itself  alone 
hardly  strong  enough,  as  we  should  suppose,  for  the  tendon  of 
so  large  a  muscle  as  the  digastric  to  work  in.  And  we  accord- 
ingly find  that  there  is  an  additional  security  in  a  strong  liga- 
ment, which  fastens  the  tendon  of  the  digastric  muscle  to  the 
hyoid  bone.  This  ligament  (which  I  have  not  represented  in 
the  figure,  because  it  would  confuse  your  view  of  the  pulley- 
action  of  the  parts)  is  sufficiently  long  to  allow  of  all  the 
freedom  of  motion  necessary  to  drawing  the  jaw  downward. 
You  see  at  once  that  one  object  of  this  arrangement  of  the  di- 
gastric muscle  is  to  secure  beauty  of  form  in  the  neck.  A 
muscle  extending  from  the  top  of  the  chest  to  the  chin  in  a 
straight  direction  would  very  effectually  draw  down  the  lower  jaw, 
but  it  would  be  a  great  deformity.  This  is  avoided  by  the  pulley- 
arrangement  of  the  digastric  .muscle.  But  this  muscle  answers 
another  purpose  besides  drawing  down  the  jaw.  If  while  the  jaw 
be  held  fast  by  muscles  which  draw  it  upward,  the  digastric 
contracts,  it  will  draw  up,  as  you  can  readily  see  by  the  Figure, 
the  hyoid  bone,  c,  and  with  it,  of  course,  the  larynx  which  is  at- 

^^•^"^••iv^^ 
OF 


208  HUMAN  PHYSIOLOGY. 


Straight  and  oblique  muscles  of  the  eye. 


tached  to  it.  Now  precisely  this  set  of  motions  occurs  when  we 
swallow.  The  mouth  is  shut  by  the  drawing  up  of  the  jaw, 
and  then  the  contraction  of  the  digastric  muscle  draws  up  the 
larynx,  as  you  can  perceive  if  you  place  your  fingers  on  the 
larynx,  or  Adam's  apple,  as  it  is  called,  when  you  perform  the 
act  of  swallowing.  The  little  muscle  in  which  the  loop  is, 
renders  some  assistance  to  the  digastric  in  thus  drawing  up  the 
hyoid  bone  and  the  larynx,  as  you  can  see  by  the  Figure. 

307.  I  will  notice  one  more  example  of  the  pulley- ar- 
rangement. It  is  in  the  eye.  There  are  six  muscles  that 
move  the  eye-ball.  Five  of  them  are  represented  in  Fig.  121. 
There  are  four  straight  muscles,  three  of  which  are  marked 

FIG.  121. 


o,  &,  c;  the  fourth  is  behind  6,  the  upper  edge  of  it  only 
being  seen  in  the  Figure.  These  muscles  are  at  their  origin  in 
the  back  part  of  the  socket  of  the  eye  arranged  round  the  optic 
nerve,  and  passing  forward  are  attached  to  the  sclerotic  coat, 
the  firm  white  coat  of  the  eye.  The  two  lateral  muscles,  ft,  and 
its  opposite,  move  the  eye  to  the  one  side  and  the  other,  and 
the  two  muscles,  a  and  c,  perform  the  up  and  down  motions. 
But  there  are  certain  oblique  rolling  motions  of  the  eyeball 
which  can  not  be  executed  by  these  straight  muscles.  For  these 
motions  two  muscles  are  provided,  one  of  which  has  a  pulley- 
arrangement,  as  represented  in  the  Figure.  This  muscle,  s,  has 
a  long  tendon  which  passes  through  a  ring  in  cartilage  in  the 
roof  of  the  socket,  and  then  turning  back  is  fastened  as  you  see 
to  the  upper  pail  of  the  eyeball.  This  muscle,  as  stated  in  the 
chapter  on  the  Nervous  System,  is  under  the  direction  of  one 
nerve  alone.  It  is  an  involuntary  muscle  which  performs  the 
insensible  rolling  motions  of  the  eyeball,  and  like  the  other  in- 
voluntary muscles  of  the  body,  is  at  work  while  we  are  asleep, 
as  well  as  when  we  are  awake.  It  is  the  muscle  which  rolls 
about  the  eye  tremulously  when  it  is  open  in  the  insensible 
state  sometimes  produced  by  disease. 


THE  MUSCLES.  209 


Opposing  muscles.    Compound  muscular  action. 


308.  Every  muscle  performing  a  motion  has  its  opposing 
muscle  or  muscles,  which  perform  the  opposite  motion.     In  the 
case  of  any  two  opposing  muscles  the  one  must  be  in  some 
measure  relaxed  while  the  other  is  in  action.     Thus  in  alter- 
nately bending  the  elbow,  and  straightening  it,  there  is  alternate 
action  and  relaxation  in  the  two  opposite  muscles  4  and  7,  as 
represented  in  Fig.  111.     So  in   moving  the  head  back  and 
forth  the  muscles  in  front  and  rear  are  alternately  contracted 
and  relaxed.     Paley  very  aptly  compares  this  to  the  action  of 
two  sawyers  in  a  pit,  as  they  move  the  saw  back  and  forth. 
The  comparison,  however,  is  not  strictly  true,  because  the  re- 
laxing muscle  is  never  wholly  relaxed.     There  is  indeed  in  every 
muscle  some  amount  of  contraction  which  is  independent  of 
action  through  the  nerves,  whether  it  be  reflex,  or  produced  by 
the  will.     For  this  reason  the  muscles  cut  off  in  amputation 
of  a  limb  retract.     So  also  if  the  muscles  on  one  side  of  the 
face  be  palsied,  the  muscles  on  the  other  side  draw  the  mouth 
to  that  side.     The  mouth  is  held  in  the  middle  of  the  face  by 
the  equal  action  of  pairs  of  muscles.     The  head,  too,  is  held  in 
equilibrium  in  the  same  way.     In  what  is  called  wry-neck,  this 
tonic  contraction,  as  it  is  sometimes  termed,  is  greater  in  the 
muscles  on  one  side  than  it  is  on  the  other.     In  some  cases  a 
cure  can  be  effected  only  by  dividing  the  contracted  muscles. 
In  strabismus,  or  squinting,  one  of  the  straight  muscles  of  the 
eyeball  contracts  too  strongly  for  its  opposing  muscle,  and  as 
in  wry-neck,  dividing  the  contracting  muscle  is  often  necessary 
to  remedy  the  difficulty. 

309.  Most  motions  are  not  performed  by  single  muscles,  but 
by  the  joint  and  agreeing  action  of  several,   and  sometimes 
many  muscles.     And  as  these  muscles  may  vary  to  a  great 
extent  in  their  degree  of  contraction,  the  motions  produced  by 
them  are  not  only  compound,  but  are  exceedingly  varied.     To 
illustrate  this  compound  and  varied  character  of  motion,  I  will 
refer  to  a  single  example  in  which  only  two  muscles  are  con- 
cerned in  the  motion.     In  Fig.  113  you  see  a  pair  of  muscles, 
one  of  which  is  marked  A,  which  extend  from  the  large  protu- 
berances behind  the  ears  to  the  top  of  the  breast-bone.     In  the 
neck  of  a  thin  muscular  person  these  muscles  are  very  promi- 
nent.    When  they  contract  equally,  the  head  is  bent  straight 
forward  in  the  middle  line   between  the  muscles,  and  a  line 
drawn  from  the  middle  of  the  forehead   down  to  the  breast- 
bone would  strike  exactly  at  the  point  where  these  two  muscles 
unite.     But  if  one  muscle  contracts  more  strongly  than  the 

18* 


210  HUMAN   PHYSIOLOGY. 


Variety  in  muscular  action.     Exemplified  in  the  tongue. 

other,  the  head  as  it  bows  forward  bows  towards  the  side  on 
which  is  the  strongest  contraction.  And  as  the  degrees  of 
contraction  in  these  two  muscles  may  be  endlessly  varied,  so 
there  may  be  an  endless  variation  in  the  degree  of  inclination 
of  the  head  to  one  side  or  the  other,  as  it  is  bent  forward.  If 
then  so  great  a  variety  in  the  direction  of  motion  may  be  pro- 
duced by  variation  in  the  degrees  of  action  in  two  muscles,  you  can 
readily  see  that  an  almost  infinite  variety  of  motion  must  result 
from  this  variation,  where  many  muscles  are  called  into  action. 

310.  I  know  not  any  part  of  the  body,  which  exemplifies  in 
so  palpable  a  manner  the  compound  and  diversified  character 
of  muscular  motion   as  the  tongue.     It  is  mostly  a  bundle  of 
muscular  fibres,  apparently  mingled  together  in  confusion,  but 
really  arranged  in  perfect  order,  so  that  it  can  be  moved  with 
great  definiteness  in  all   directions,  forward,  backward,  upward, 
downward,  to  either  side,  and  in  all  intermediate  directions.     If 
you  stand  before  a  glass,  and  opening  your  mouth,  move  the 
tongue  rapidly  about  in  all  these  directions,  you  think  of  a  har- 
lequin performing  his  antics.     But  all  this  wonderful  variety  of 
movement  is  produced  in  obedience  to  the  definite  action  of 
nerves,  whose  fibres  are  mingled  with  the  muscular  fibres  of  the 
tongue.     And  in  order  to  produce  each  motion  there  is  an  agree- 
ment of  action  not  between  merely  many  of  these  fibres,  but 
between  multitudes  of  them. 

311.  With  the  view  which  I  have  given  you  of  the  compound 
and  varied  character  of  muscular  motion,  you  are  prepared  to 
take  a  general  survey  of  the  muscular  system.     For  this  pur- 
pose I  call  your  attention  to  a  side  view  of  the  muscles  of  the 
body  as  presented  in  Fig.  122.     I  must  premise,  that  you  can 
get  no  idea  from  this  Figure  of  the  number  of  the  muscles  in 
the  body,  for  you  see  here  only  the  outer  layer  of  muscles,  and 
there  are  many  muscles  concealed  by  them.     You  observe  that 
they  are  of  various  shapes  and  sizes,  according  to  the  motions 
which   they  are  designed  to  produce,  and  the  circumstances 
in  which  they  are  placed.     They  are  round,  long,  short,  flat, 
fan-shaped,   circular,    serrated,    &c.      I   will   point   out   some 
of  them.     At   a  is    the  very   large    muscle  that   makes   the 
fleshy  prominence   at  the  upper   part   of  the  arm,  and   the 
office  of  which  is  to  raise  the  arm,  carrying  it  out  from  the 
body.     You  observe  that  its  fibres  are   not  all  arranged  alike 
but  lie  in  different  directions.     The  result  is,  that  while  the 
arm  is  raised  by  the  muscle  as  a  whole,  it  may  be  carried  at 
the  same  time  forward  or  backward  by  the  varying  action  of 


THE   MUSCLES. 


211 


External  layer  of  the  muscles  of  the  body. 


FIG.  122. 


MUSCLES    OF   THE    BODY. 


212  HUMAN  PHYSIOLOGY. 

General  description  of  the  muscles  in  various  parts. 

these  different  fibres.  There  are  many  of  the  muscles  of  the 
body  which  are  made  thus  to  produce  various  results  by 
variation  of  the  action  of  different  parts  of  the  same  muscle. 
And  the  regulation  of  this  variation  by  the  nerves  is  one  of 
the  most  wonderful  and  mysterious  things  which  we  find  in 
our  study  of  the  nervous  system.  For  each  fibre  in  the  cases 
referred  to  is  told,  as  we  may  express  it,  just  how  much  it  must 
do  in  order  to  produce  the  requisite  general  motion  of  the 
muscle.  It  is  manifestly  much  more  wonderful  thus  to  pro- 
duce various  but  accurately  graduated  contraction  in  different 
parts  of  the  muscle,  than  to  produce  an  uniform  contraction  in 
all  its  fibres. 

312.  I  go  on  with  my  notice  of  the  particular  muscles.  At 
b  is  the  biceps  muscle,  which  bends  the  forearm  upon  the  arm, 
and  at  c  is  another  muscle  that  assists  the  biceps.  At  e  is  the 
large  muscle  in  the  back  of  the  arm,  which  acts  in  opposition 
to  the  biceps,  and  straightens  the  forearm  upon  the  arm.  At 
d  is  a  muscle  which  rolls  the  radius  outwards,  and  thus  turns 
the  palm  of  the  hand  upward  as  seen  in  the  Figure.  At  g  is  a 
very  large  broad  muscle  coming  from  the  whole  length  of  the 
back,  and  at  the  axilla  or  arm-pit,  its  fibres  are  collected, 
twisted,  and  folded  upon  each  other.  The  muscle  is  fastened 
by  a  stout  tendon  to  the  upper  and  back  part  of  the  bone  of 
the  arm,  and  its  office  is  to  pull  the  arm  backwards  and  down- 
wards. At  h  is  a  serrated  muscle,  which  rising  from  the  ribs, 
goes  to  the  shoulder-blade,  and  serves  to  draw  the  shoulder- 
blade  forwards.  At  i  is  one  of  the  broad  muscles  of  the  ab- 
domen. At  I  and  k  are  two  large  muscles  that  move  the 
thigh.  At  o  and  jt?,  as  seen  on  the  right  thigh,  and  at  w,  as 
seen  on  the  left,  are  three  large  muscles,  which  are  fastened  to 
the  kneepan,  and  serve  to  throw  the  leg  forward  as  described 
in  §  304.  At  q  is  the  tendon  that  forms  the  outer  hamstring, 
and  at  r  are  the  two  tendons  which  form  the  inner  one.  The 
muscles  to  which  these  tendons  belong,  serve  to  bend  the  leg 
upon  the  thigh,  drawing  it  upward  and  backward.  At  5  is 
the  muscle  which  makes  the  bulk  of  the  calf  of  the  leg.  It 
lifts  the  heel  upward  and  backward,  and  it  is  seen  in  action  m 
the  right  leg  of  the  Figure.  Its  strong  tendon  which  is  at- 
tached to  the  top  of  the  heel  bone  is  called,  on  account  of  its 
strength,  the  tendon  of  Achilles.  This  muscle  is  in  Fig.  109, 
the  power  P  which  raises  the  weight  of  the  body,  W,  on  the 
fulcrum,  F,  as  the  heel  is  raised  from  the  ground  in  walking. 
313.  In  Fig.  123  you  have  a  rear  view  of  the  muscles.  At 


THE  MUSCLES. 


213 


Rear  view  of  the  external  layer  of  the  muscles. 


FIG.  123. 


c.... 


REAR    VIEW    OF    THE    MUSCLES. 


214  HUMAN  PHYSIOLOGY. 

Some  muscles  are  very  small.     Symmetrical  arrangement  of  the  muscles. 

a  is  a  very  broad  muscle,  which  rising  from  the  back  is  attached 
to  different  parts  of  the  shoulder-blade.  You  can  see  that 
this  irregularly  shaped  muscle,  will  move  the  shoulder-blade 
variously,  according  to  the  various  action  of  the  different  fibres 
of  the  muscle,  which  run  in  so  different  directions.  At  c  you 
see  the  rear  part  of  the  muscle  that  raises  the  arm.  At  b  is 
the  extensive  muscle  that  you  saw  in  Fig.  122  at  </,  which 
draws  the  arm  backward.  At  e  is  a  large  muscle  that  draws 
the  thigh  backward.  At  g,  h,  and  /  are  the  muscles  whose 
tendons  form  the  two  hamstrings.  At  i  is  the  muscle  that 
forms  the  calf  of  the  leg,  and  raises  the  heel. 

314.  I  have  thus  described  to  you  a  few  of  the  principal 
muscles  in  the  body,  that  you  may  have  some  idea  of  the  modes 
in  which  they  act,  and  the  manner  in  which  they  are  arranged. 
Those  which  I  have  described  are  all  muscles  of  considerable 
size.     But  there  are  some  exceedingly  small  muscles  in  the 
body,  producing  some  very  delicate  motions.     For  example,  all 
the  variations  in  the  note  of  the  voice  result,  as  you  will  see  in 
the  Chapter  on  the  Voice,  from  the  variation  of  tension  of 
the  vocal  ligaments,  which  is  regulated  by  certain  very  small 
muscles.     As  the  laborer  sings  over  his  work,  great  is  the  con- 
trast between  the  delicate  action  of  these  little  muscles,  and  the 
strong  action  of  the  muscles  of  his  stalwart  arm.     A  variation 
of  less  than  a  hair's  breadth  in  the  contraction  of  the  muscles 
of  the  vocal  ligaments  suffices  to  produce  an  appreciable  differ- 
ence in  the  note  of  the  voice. 

I  have  thus  far  spoken  of  the  bones  especially  as  being 
moved  by  the  muscles.  But  other  parts  are  moved  by  them 
also.  In  the  case  of  the  voice,  just  alluded  to,  the  little  muscles 
move  cartilages  to  which  the  vocal  ligaments  are  attached. 
The  tongue  and  the  palate  are  moved  by  muscles.  Muscles 
move  the  skin.  In  man-  this  is  generally  very  much  confined 
to  the  face.  The  mouth,  the  eyelids,  the  eyebrows,  &c.,  are 
moved  by  muscles.  In  many  animals  the  skin  is  moved  ex- 
tensively by  muscles,  as  for  example  when  the  horse  shakes  his 
skin  to  get  rid  of  the  biting  flies. 

315.  In  the  arrangement  of  the  muscles  great  regard  has 
been  paid  by  the  maker  of  our  bodies  to  convenience  and  sym- 
metry, and  not  merely  to  mechanical  advantages.     Thus,  the 
muscles   moving  the  fingers  are  mostly  placed  in  the  forearm, 
while  the  slender  tendons  pass  over  the  surface  of  the  bones  in 
the  wrist.     The  flowing  outline  of  the  arm  is  thus  secured,  and 
the  hand  is  made  a  light,  and  at  the  same  time,  a  strong  ap- 


THE   MUSCLES.  215 


Contrivances  in  muscles  and  tendons  of  the  hand  and  foot. 

paratus.  The  same  can  be  said  substantially  of  the  arrange- 
ment of  the  muscles  and  tendons  in  the  leg  and  foot.  There 
is  one  arrangement  in  the  foot  which  is  worthy  of  especial  no- 
tice. There  is  a  muscle  in  the  fleshy  part  of  the  leg,  which  by 
a  long  tendon,  divided  in  the  foot  into  four  tendons,  bends  the 
last  joints  of  the  toes.  There  is  also  a  short  thick  muscle  in 
the  bottom  of  the  foot  which  joins  the  tendons  of  the  first 
named  muscle,  and  assists  it  in  bending  the  toes.  It  is  as  if 
two  different  sets  of  men  were  placed  in  two  different  positions, 
with  ropes  arranged  so  as  to  pull  in  the  same  direction.  The 
question  arises,  why  the  toes  are  not  bent  by  a  single  muscle, 
lodged  conveniently  in  the  fleshy  part  of  the  leg.  The  reason 
probably  is,  that  the  muscle  placed  in  the  sole  of  the  foot  is 
needed  there  as  a  filling  up  in  the  arch  of  the  foot,  and  so  the 
force  necessary  to  bend  the  toes  is  divided  between  the  two 
positions. 

316.  There  is  another  contrivance  in  this  muscle  that  bends  the 
toes  which  I  will  notice  here.  Its  four  tendons  pass  to  the  last 
bones  in  the  toes,  and  in  doing  so  they  go  through  the  tendons 
of  the  muscle  that  bends  the  second  joints.  These  latter  divide 
at  their  ends  where  they  join  the  bones  for  this  purpose.  A 
similar  arrangement  also  is  made  in  the  fingers  for  the  tendons 
of  the  second  and  third  joints.  This  is  represented  in  Fig.  124, 

FIG.  124. 


in  which  e  is  the  tendon  which  goes  to  the  last  bone  c  through 
the  division  in/,  which  goes  to  the  second  bone  b.  It  is  mani- 
fest that  this  is  the  best  way  of  packing  the  tendons,  as  we  may 
express  it.  Any  other  conceivable  arrangement  would  add  to 
the  bulk  of  the  finger.  As  they  are  represented  in  the  figure 
they  are  raised  up,  instead  of  being  closely  packed  down  upon 
the  bone,  as  they  are  in  reality. 

317.  I  have  already  alluded  to  the  fact  that  many  muscles 
unite  in  producing  most  of  the  movements  of  the  body,  and 
that,  as  they  vary  in  the  degrees  of  their  contraction,  the 
variety  of  motion  resulting  from  both  these  causes,  is  exceed- 


216  HUMAN  PHYSIOLOGY. 

Complicated  action  of  associated  muscles. 

ingly  great.  I  will  now  call  your  attention  more  particularly 
to  these  points,  as  you  can  more  readily  appreciate  them  after 
the  general  view  which  you  have  taken  of  the  muscular  system. 
Even  when  only  a  part  of  the  body  is  put  in  motion,  there  are 
often  many  muscles  engaged  in  the  act.  Take,  for  example, 
the  act  of  swallowing,  which  I  have  described  in  §  78  in  the 
Chapter  on  Digestion.  In  this  compound  act  the  muscles  of  the 
jaw  close  the  mouth,  the  tongue  thrusts  the  food  back  into 
the  throat,  the  digastric  muscle  .(§  306),  pulls  up  the  larynx, 
and  the  epiglottis  is  at  the  same  time  shut  down  by  muscles 
upon  the  opening  into  the  larynx,  to  let  the  food  slide  over  it. 
In  speaking  and  singing  the  action  of  the  muscles  is  much  more 
complicated  than  in  the  act  of  swallowing.  The  muscles  of  the 
chest  work  the  bellows  of  the  organ  (for  such  is  the  relation  of 
the  chest  to  the  musical  instrument,  the  larynx,)  the  muscles  of 
the  vocal  ligaments  put  them  in  the  state  of  tension  required 
to  produce  the  note  intended,  the  muscles  of  the  epiglottis  raise 
it  to  let  the  sound  out,  and  the  muscles  of  the  throat,  palate, 
tongue,  and  lips,  give  articulation  to  the  sound  as  it  comes  from 
the  larynx.  And  observe,  that  some  of  the  same  parts  are  en- 
gaged in  the  act  of  speaking  that  are  engaged  in  that  of  swal- 
lowing, but  are  put  in  different  positions  for  the  two  acts. 
Thus,  the  epiglottis  is  raised  up  when  we  speak,  and  is  shut 
down  when  we  swallow,  and  the  larynx  is  raised  up  when  we 
swallow,  and  is  drawn  down  again  when  we  speak.  And  how 
quickly  we  pass  from  the  one  act  to  the  other,  as  we  mingle 
our  talking  and  eating  together !  And  we  do  it  with  such 
facility  and  precision,  that  it  is  a  very  rare  accident  that  a  crumb 
or  a  drop  slips  into  the  larynx.  Observe  farther,  that  when  we 
take  a  breath,  as  well  as  when  we  speak,  the  epiglottis  must  be 
raised,  the  air  passing  in,  instead  of  passing  out  as  in  speaking. 
The  parts,  therefore,  are  often  engaged  in  these  different  acts, 
not  only  distinct  from  each  other,  but  inconsistent  with  each 
other  also,  and  they  change  from  one  of  these  acts  to  another 
so  readily,  that  as  we  eat,  and  breathe,  ana!  talk,  we  are  con- 
scious of  no  disturbance,  and  scarcely  ever  of  any  effort  in  the 
change.  No  change  of  action  in  any  machinery  of  man's  in- 
vention can  be  at  all  compared  with  this  in  the  precision  and 
facility  of  the  change,  much  less  in  its  complicated  character. 

318.  But  if  there  be  complication  and  variety  of  action  when 
but  one  part  of  the  body  is  put  in  motion  by  the  muscles,  there 
will  be  vastly  more  when  the  muscles  of  the  body  as  a  whole 
are  brought  into  action.  If  you  look  at  Fig.  122,  you  see  the 


THE   MUSCLES.  217 


Constant  change  in  complicated  muscular  movements. 


muscles  generally  in  more  or  less  action,  and  the  action  of  each 
one  has  its  particular  relation  to  the  attitude  assumed.  If  now 
the  attitude  be  varied,  this  particular  relation  of  each  muscle 
must  be  varied  also.  If,  for  example,  the  right  foot  be  carried 
forward  so  as  to  bring  the  weight  of  the  body  on  to  that  foot, 
instead  of  the  left,  on  which  it  now  rests,  as  represented  in  the 
Figure,  all  the  muscles  of  the  frame  will  have  a  different  rela- 
tion in  their  action.  And  not  only  this,  but  while  the  body  is 
changing  from  the  one  attitude  to  the  other,  there  will  be  a 
continual  change  of  this  relation.  At  no  one  moment  during 
the  act  or  motion,  which  changes  the  attitude,  will  the  state  of 
contraction  in  each  muscle  be  precisely  the  same,  that  it  is  at 
any  other  moment.  Thus,  the  state  of  the  muscles  in  the  be- 
ginning of  the  change  of  attitude  is  altogether  different  from 
what  it  is  when  the  movement  is  half  accomplished.  And  the 
same  can  be  said  of  any  other  two  points  in  the  progress  of  the 
movement.  The  same  is  true  of  any  other  general  action 
of  the  muscles.  Thus,  if  one  is  pulling  with  his  feet  braced,  the 
muscles  do  not  remain  in  the  same  relative  condition  all  the 
time,  but  as  the  body  which  is  pulled  yields,  the  relative  tension 
of  the  muscles  is  changed  every  moment.  But  there  is  no 
movement  which  exemplifies  this  change  of  relative  condition 
of  the  muscles  so  well  as  that  of  balancing.  If  with  the  views 
which  I  have  presented  in  your  mind,  you  observe  some  one 
who  is  skillful  in  balancing,  you  will  be  impressed  with  the  ever 
changing  but  precisely  regulated  degree  of  tension  in  the  differ- 
ent muscles,  and  with  the  variety  of  combination  in  their 
action. 

319.  I  will  not  comment  to  any  extent  upon  the  general 
movements  and  attitudes  of  the  body.  But  I 
will  here  simply  call  your  attention  to  one 
mode  of  action,  in  which  a  large  number  of 
the  muscles  are  called  into  play,  on  account  of 
its  analogy  to  an  expedient  often  used  in  me- 
chanics. I  refer  to  what  is  called  the  toggle- 
joint.  This  I  will  explain.  Let  c,  a,  and  c,  6, 
represent  two  bars  connected  together,  like  a 
carpenter's  folding  rule,  by  a  hinge  or  joint  at 
c.  Suppose  the  two  ends,  a  and  6,  to  be  fitted 
into  the  two  blocks  represented  in  the  Figure. 
If  now  the  block  at  b  is  fixed,  and  the  block  at 
a  is  movable,  and  force  be  applied  to  the  joint 
c  carrying  it  towards  c?,  the  block  at  a  will  be  TOGGLE-JOINT. 

19 


c  carr 


218  HUMAN    PHYSIOLOGY. 

Examples  of  the  toggle-joint  in  muscular  movements. 


pressed  upward  with  considerable  power.  If  on  the  other 
hand,  the  block  at  b  is  movable,  and  that  at  a  is  fixed,  the  block 
at  b  will  be  pressed  downward.  We  see  this  latter  form  of  the 
contrivance  applied  in  printing  presses.  In  the  human  body 
this  toggle-joint  is  used  in  both  ways.  When  one  stoops  to 
take  a  heavy  weight  upon  his  back  or  shoulder,  he  puts  both 
the  knee  and  the  hip-joints  into  the  condition  that  the  toggle- 
joint  is  when  it  is  bent ;  and  then  as  he  straightens  up,  the 
weight  is  raised  by  an  action  of  the  joints  precisely  similar  to 
that  of  the  toggle-joint  in  machinery.  In  the  case  of  the  knee, 
the  straightening  of  the  joint  is  done  by  the  muscles  on  the 
front  part  of  the  thigh,  that  draw  up  the  kneepan  with  the 
tendon  attached  to  it.  This  is  using  the  principle  of  the  toggle- 
joint  in  pressing  upward.  It  is  also  sometimes  used  in  pressing 
downward.  In  crushing  any  thing  with  the  heel,  we  give  great 
force  to  the  blow  on  the  principle  of  the  toggle-joint,  by  flexing 
the  knee  and  straightening  the  limb  as  we  bring  down  the  heel 
upon  the  thing  to  be  crushed.  In  pushing  any  thing  before  us, 
we  bend  the  elbow  as  preparatory  to  the  act,  and  then  thrust 
the  arm  out  straight,  thus  exemplifying  the  toggle-joint.  The 
horse  gives  great  force  to  his  kick  in  the  same  way.  The  great 
power  exerted  by  beasts  of  draught  and  burden  is  to  be  referred 
very  much  to  the  principle  of  the  toggle-joint.  When  a  horse 
is  to  draw  a  heavy  load,  he  bends  all  his  limbs,  especially  the 
hinder  ones,  and  then  as  he  straightens  them,  he  starts  the 
load.  In  this  case  the  ground  is  the  fixed  block  of  the  me- 
chanism, the  body  of  the  horse  to  which  the  load  is  attached  is 
the  movable  one,  and  his  limbs  are  so  many  toggle-joints.  By 
this  application  of  the  principle  we  see  draught  horses  move 
very  heavy  loads.  "So,  (admitting  fable  to  be  fact,")  says  Dr. 
Griscom,  "  when  the  farmer,  in  answer  to  his  petition  for  assist- 
ance, was  commanded  by  Hercules  to  exert  himself  to  raise  his 
wagon  from  the  pit,  he  placed  his  shoulder  against  the  wheel, 
and  drawing  his  body  up  into  a  crouching  attitude,  whereby  all 
his  joints  were  flexed,  and  making  his  feet  the  fixed  points,  by 
a  powerful  muscular  effort,  he  straightened  the  toggle-joints  of 
his  limbs,  and  the  wheel  was  raised  from  its  bed  of  miry  clay. 
His  horses  at  the  same  moment  extending  their  joints,  the 
heavily  laden  wagon  was  carried  beyond  the  reach  of  farther 
detention." 

320.  The  hand  is  the  most  wonderful  of  all  parts  of  the 
body,  in  regard  to  variety  and  complication  of  movement 
There  are  over  lifty  muscles,  which  are  engaged  in  the  various 


TIIK    MrrVM-lS.  219 


Great  vnrioty  of  notion  in  tlie  muncloi  of  tho  hnnd. 


motions  of  tho  upper  extremity,  all  of  which,  of  course,  have 
more  or  less  reference  to  (In-  hand.  Indeed  the  hand  is  the 
part,  of  (lie  upper  extremity  to  which  all  ils  oilier  parts  are 
tributary,  and  therefore  we,  may  properly  consider  all  these 
muscles  as  in  :i  great  measure  belonging  to  the  hand.  1C  now 
you  call  to  mind  the  fad,  that  each  one  of  these  muscles  can 
vary  the  (tinoiint  of  its  contraction  in  all  decrees,  from  the  most 
powerful  action  down  to  the  slightest  movement,  you  cau 
readily  sec  that  fifty  muscles  with  this  power  of  variation  can 
produce  an  almost  endless  ^number  of  combinations  of  motion. 
The  variety  would  be  exceeding I y  great,  even  if  every  muscle, 
whenever  it  acted,  had  always  the  same  amount  of  contraction. 
l>ut  the  power  of  varying  the  amount,  of  contraction  multiplies 
the  variety  to  an  inconceivable  extent. 

321.  If  you  watch  the  movements  of  the  hand  with  its  fingers, 
as  you  exercise,  it  in  a  great  variety  of  motions,  yon  cau  get 
some  idea  of  its  capabilities  in  this  respect.  If,  too,  you  ob- 
serve its  movements  in  different  individuals  in  all  kinds  of  labor 
and  handiwork,  vou  will  be  still  more  impressed  with  the  ex- 
treme variety  of  its  movements.  It  is  capable  of  performing  tho 
heaviest  and  rudest,  work,  and  at  the  same  time  the  most  deli- 
cate. How  wide  the  difference  between  wielding  the  ax  or  the 
sledge-hammer,  and  moving  the  engraver's  tool  in  some  of  the 
finest,  productions  of  his  art!  How  firm  is  its  grasp  of  the 
hammer,  and  yet  how  gentle  is  its  pressure  upon  the  graver,  as  j(, 
moves  it,  in  almost,  invisible  lines!  The  shape  of  the  hand,  with 
its  fingers  of  unequal  length,  and  its  thumb  opposite  to  them, 
capable  of  touching  the.  tip  of  each  of  the  fingers,  or  all  of  them 
ton-ether,  enables  it  to  accommodate  itself  to  a  vast,  variety  of 
shapes  and  sixes  of  objects;  and  its  delicate  papilhe,  tilled  with 
nerves  and  arranged  in  rows,  as  you  can  see,  on  the  tips  of  the 
fingers  under  the  skin,  endow  this  wonderful  instrument  with  a 
sensibility  which  guides  its  muscular  movements.  When, 
therefore,  we  OOMUier  the  almost  endless  variety  of  its  motions, 
the  delicacy  and  accuracy  of  its  sense  of  touch,  and  besides 
these,  the  force  and  grace  with  which  it  acts  in  the  expression 
of  thought,  and  feeling,  we  hardly  wonder  that  some  have  fixed 
Upon  tin-  hand  as  man's  distinguishing  characteristic,  and  we 
are  impressed  with  the  thought,  that  it  is  a  fitting  instrument, 
•>f  work  and  expression  for  that  mind,  which  is  tho  image  of 
<Jod  in  man. 

^'J'2.  Having  thus  taken  a  survey  of  the  muscular  system,  let 
iis  look  fora  moment  at  the  whole  machinery,  aa  it  works  when 


220  HUMAN   PHYSIOLOGY. 

Nice  adjustment  of  the  muscular  movements.     How  effected. 

it  is  engaged  at  the  same  time  in  some  general  movement,  and 
in  some  special  movements  of  some  departments  of  it.  Look, 
for  example,  at  some  one  who  is  busied  in  conversation  while  ho 
is  walking,  and  is  perhaps  at  the  same  time  twirling  something 
in  different  directions  in  his  fingers.  Here  you  have  a  general 
action  of  the  muscles  as  described  in  §  318,  and  with  it  a  par- 
ticular action  of  two  sets  of  muscles  in  two  different  parts  of  the 
body ;  and  yet  so  well  do  the  nerves  regulate  these  various 
movements,  that  there  is  no  disturbance  or  confusion  in  the 
complicated  machinery.  While  the  muscles  of  the  arm  and 
fingers  are  at  work  executing  their  diversified  motions,  the  little 
muscles  of  the  larynx  are  ever  varying  the  notes  of  the  voice, 
and  the  muscles  of  articulation  are  putting  that  voice  into  every 
variety  of  shape.  And  while  these  movements  are  going  on  in 
these  particular  parts  of  the  system,  the  machinery  as  a  whole 
is  executing  one  of  its  grand  general  movements.  And  besides 
all  this,  the  muscles  of  respiration  are  at  work  all  the  while,  in- 
troducing air  into  the  lungs  to  change  the  blood,  and  forcing  it 
out  through  the  trachea  to  make  th*  vocal  ligaments  vibrate ; 
and  that  compound  muscle  the  heart  is  pumping  at  the  rate  of 
seventy  times  a  minute  sending  the  blood  through  its  tubes 
every  where  ;  and  if  there  be  any  food  in  the  stomach,  the  mus- 
cular fibres  of  that  organ  are  at  work  churning  the  food  to 
make  more  blood.  How  complicated  is  the  machinery  that  per- 
forms all  these  operations,  and  yet  with  what  precision  every  mus- 
cle, nay,  every  individual  fibre  works  in  obedience  to  the  nerves  ! 
323.  The  question  arises,  how  in  all  the  diversified  action  of 
the  muscles  their  nice  adjustment  is  effected.  How  do  the 
muscles  know,  as  we  may  express  it,  just  how  much  to  do  in 
each  movement?  When,  for  example,  you  reach  your  hand 
up  to  touch  some  object,  how  does  each  muscle  know  just  what 
degree  of  contraction  is  necessary  to  make  the  hand  go  with 
precision  to  the  particular  point  arrived  at  ?  And  so  when  one 
is  playing  on  an  instrument  with  the  fingers,  as  the  piano,  vary- 
ing their  pressure  continually  in  accordance  with  the  desired  loud- 
ness  of  the  sound,  how  does  each  muscle  know  just  what  amount 
of  contraction  is  required  of  it  in  each  movement  ?  Though  the 
senses  of  vision  and  touch  afford  some  assistance  in  the  guidance 
of  muscular  action  in  such  cases,  something  else  is  manifestly 
necessary.  Sir  Charles  Bell,  therefore,  supposes  that  there  is 
what  he  calls  a  muscular  sense,  which  acts  as  a  guide  to  the 
muscles,  in  connection  with  the  senses  of  sight  and  touch.  In 
some  cases  it  is  the  sole  guide.  On  this  subject,  Sir  Charles 


THE   MUSCLES.  221 


Sir  Charles  BelPs  description  of  the  muscular  sense. 


says,  "  When  a  blind  man,  or  a  man  with  his  eyes  shut,  stands 
upright,  neither  leaning  upon  or  touching  aught ;  by  what 
means  is  it  that  he  maintains  the  erect  position  ?  The  sym- 
metry of  his  body  is  not  the  cause ;  the  statue  of  the  finest  pro- 
portion must  be  soldered  to  its  pedestal,  or  the  wind  will  cast  it 
down.  How  is  it,  then,  that  a  man  sustains  the  perpendicular 
posture,  or  inclines  in  due  degree  towards  the  winds  that  blow 
upon  him  ?  It  is  obvious  that  he  has  a  sense  by  which  he 
knows  the  inclination  of  his  body,  and  that  he  has  a  ready  ap- 
titude to  adjust  it,  and  to  correct  any  deviation  from  the  per- 
pendicular. What  sense  then  is  this  ?  for  he  touches  nothing, 
and  sees  nothing  ;  there  is  no  organ  of  sense  hitherto  observed 
which  can  serve  him,  or  in  any  degree  aid  him.  Is  it  not  that 
sense  which  is  exhibited  so  early  in  the  infant,  in  the  fear  of 
falling  ?  Is  it  not  the  full  development  of  that  property  which 
was  early  shown  in  the  struggle  of  the  infant  while  it  yet  lay  in 
the  nurse's  arms  ?  It  can  only  be  by  the  adjustment  of  muscles 
that  the  limbs  are  stiffened,  the  body  firmly  balanced,  and  kept 
erect.  There  is  no  oth«*  source  of  knowledge,  but  a  sense  of 
the  degree  of  exertion  in  his  muscular  frame,  by  which  a  man 
can  know  the  position  of  his  body  and  limbs,  while  he  has  no 
point  of  vision  to  direct  his  efforts,  or  the  contact  of  any  exter- 
nal body.  In  truth,  we  stand  by  so  fine  an  exercise  of  this 
power,  and  the  muscles  are,  from  habit,  directed  with  so  much 
precision,  and  with  an  effort  so  slight,  that  we  do  not  know 
how  we  stand.  But  if  we  attempt  to  walk  on  a  narrow  ledge, 
or  stand  in  a  situation  where  we  are  in  danger  of  falling,  or  rest 
on  one  foot,  we  become  then  subject  to  apprehension  ;  the  actions 
of  the  muscles  are,  as  it  were,  magnified  and  demonstrative  of 
the  degree  in  which  they  are  excited." 

324.  It  is  obvious  then  that  this  muscular  sense  informs  the 
mind  of  the  changing  postures  of  the  body,  and  guides  the 
muscles  in  effecting  these  postures.  And  it  has  a  particular  set 
of  nervous  fibres  devoted  to  it,  separate  from  those  fibres  which 
excite  the  muscles  to  action,  though  they  are  ordinarily  in- 
closed in  the  same  sheath.  This  sense,  it  may  also  be  remarked, 
is  a  source  of  pleasure,  as  well  as  the  other  senses.  The  mo- 
tions of  the  body  are  attended  with  a  senso  of  enjoyment,  which 
lightens  labor,  and  adds  zest  to  our  active  sports.  The  enjoy- 
ment of  the  muscular  sense  we  see  constantly  exemplified  in  the 
gambols  of  animals.  It  may  be  still  further  remarked,  that  this 
sense  is  capable  of  being  educated  like  the  other  senses.  But 
of  this  I  shall  speak  in  another  place. 

19* 


222  HUMAN  PHYSIOLOGY. 

All  thought  and  feeling  communicated  by  muscles. 


CHAPTER    XIII. 

LANGUAGE   OP  THE  MUSCLES 

325.  As  THE  nerves  of  sensation  are  the  inlets  of  all  know- 
ledge to  the  mind,  the  nerves  of  motion  are  the  outlets  by 
which  all  knowledge  is  communicated.     Thought  and  feeling 
are  expressed  only  by  muscular  motion.     It  is  true  that  there 
are  some  accompanying  and  subordinate  modes  of  expression, 
as  the  flowing  of  tears,  the  action  of  the  capillaries  producing 
blushing,    and   the   paleness   occasioned   by  fear.     But  these 
could  not  of  themselves  alone  communicate  thought  and  feel- 
ing, and  can  do  so  only  by  being  associated  with  other  signs. 
They  only  add  force  to  the  expression  already  produced   by 
muscular  action.     Indeed  they  are  signs  which  can  not  be  un- 
derstood, unless  muscular  action  interpret  them.     Thus  if  tears 
flow,  we  know  not  whether  they  are  tears  of  joy  or  sorrow,  e-x- 
cept  as  the  expression  of  the  countenance  informs  us  ;  and  ex- 
pression,  as  I  shall  show  you  in  this  chapter,  is  wholly  the 
result  of  the  action  of  muscles.     So  too,  the  muscles  of  the  face 
tell  us,  whether  the  blush  that  mantles  there  is  the  blush  of 
shame,  or  of  modesty.     And  when  we  see  paleness  caused  by 
fear,  we  know  that  this  is  the  cause,  only  from  the  expression 
of  the  countenance  and  the  attitude  of  the  body,  which   may 
very  properly  be  called  the  expression  of  the  body,  though  it  is 
much  less  marked  than  the  expression  of  the  countenance. 

326.  It  is  by  the  voice  chiefly  that  thought  and  feeling  are 
communicated.     And  every  variation  of  note,  or  of  articulation, 
is  caused,  as  I  shall  show  you  in  the  next  chapter,  by  the  action 
of  muscles.     When  the  muscles  of  the  hand  communicate  to 
others  thought  and  feeling  by  writing,  they  merely  translate 
the  language  of  the  muscles  of  the  vocal  organs  into  conven- 
tional signs.     Leaving  the  language  of  these  vocal  muscles  for 
another  chapter,  I  shall  in  this  notice  the  language  of  the  other 
muscles  of  the  body  and  especially  of  those  of  the  foce. 

327.  As  we  watch  an  animated  speaker,  we  see  that  it  is  not 
the  face  alone,  that  adds  force  to  his  utterances  by  its  corres- 
ponding expressions.     Various  parts  of  the  body  in  a  measure 
do  the  same  thing.     The  head  is  nodded  or  shaken,  the  shoulder 
is  shrugged,  the  foot  is  stamped,  and  above  all,  the  hand  exe- 


THE   LANGUAGE   OF  THE   MUSCLES.  223 


Extent  of  range  of  the  language  of  the  muscles. 


cutes  a  great  variety  of  motions,  in  correspondence  with  th« 
thoughts  and  feelings  which  the  mouth  utters.  Sometimes  too, 
the  whole  frame  is  brought  into  action.  The  gestures  and  the 
attitudes,  which  are  but  gestures  of  the  whole  body,  are  im- 
portant aids  to  the  orator  in  conveying  his  thoughts  and  feelings 
into  the  minds  of  his  auditors. 

328.  This  language  of  the  muscles  is  used  to  a  greater  ex- 
tent than  we  are  conscious  of  in  our  ordinary  intercourse.     We 
are  not  aware  how  much  we  communicate  in  this  way.     This 
language  is  by  no  means  confined  to  those  palpable  acts  which 
this  subject  suggests  at  once  to  the  mind, — the  broad  laugh 
of  merriment;  the  sighing,  and  sobbing,  and  weeping  of  grief ; 
the  stamping  of  the  foot  in  anger  ;  the  pointing  of  the  finger  in 
calling  attention  to  any  particular  subject ;  the  gesture  used  in 
beckoning  one  to  come  to  you,  &c.     But  it  includes  numerous 
little  and  scarcely  observed  motions,   which   in  great  variety 
add  to  the  significance  of  the  words  which  we  utter.     And  in 
the  case  of  the  countenance,  far  more  is  communicated  in  the 
aggregate  by  the  constant  gentle  play  of  the  muscles,  than  by 
the  broader  and  more  palpable  expressions,  which  are  occasion- 
ally produced  by  their  stronger  action.     The  deaf  mute  can 
gather  from  the  language  of  the  muscles,  as  it  accompanies  the 
voice  that  he  can  not  hear,  much  more  information  as  to  the 
passing  conversation   than  one  would  suppose  that  he  could. 
And  the  full  capabilities  of  this  language  we  can  only  learn,  by 
observing  to  what  wonderful  extent  the   deaf  and  dumb  can 
communicate  with  each  other  by  the  use  of  natural  signs,  with- 
out any  aid  from  those  which  are  artificial.* 

329.  While  in  man  the  muscles  of  the  face  are  the  chief 
agents  of  expression,  in  other  animals  the  very  limited  expres- 
sion of  which  they  are  capable,  is  chiefly  effected  by  other  parts 
of  the  body.     For  example,  the  dog  wags  his  tail,  the  cat  puts 
up  her  back,  the  game-cock  spreads  out  his  ruff  of  feathers  on 
his  head,  &c.     Rage  is  almost  the  only  passion  which  can  be 
expressed  by  animals  in  the  countenance.     They  can  snarl,  but 

*  I  wns  much  struck  with  an  illustration  of  the  great  range  of  the  language  of  natural 
signs,  in  an  exhibition  made  many  years  ago  by  the  lamented  Gallaudet  before  the  legisla- 
ture of  Massachusetts.  Previous  to  exhibiting  the  attainments  of  his  pupils,  he  requested, 
that  if  any  deuf  and  dumb  person  who  had  not  been  educated  in  an  asylum  were  present, 
his  friends  would  bring  him  forward,  thut  he  might  show  how  much  could  be  communi- 
cated by  natural  signs.  A  man  came  forward,  and  Mr.  Gallaudet  learned  from  him  by 
natural  signs  alone  such  facts  as  these, — the  place  of  his  residence,  the  fact  that  his  parents 
were  living,  the  number  of  his  brothers  and  of  his  sisters,  the  fact  that  he  had  seen  Mr. 
G.  before  in  a  certain  place,  ficc.  Any  one,  it  may  be  remarked  in  this  connection,  who 
has  been  engaged  in  teaching  the  deaf  and  dumb,  and  who  has,  therefore,  become  skilled 
in  the  use  of  sign-language,  can  converse  quite  readily  by  signs  with  foreigners  from  any 
purt  of  the  wort. 


224  HUMAN  PHYSIOLOGY. 

Principal  muscles  used  in  smiling  and  laughter. 


they  can  not  laugh  or  cry.  Hence  it  has  been  said,  that  man 
can  be  very  properly  distinguished  from  other  animals  by 
calling  him  "  a  laughing  and  crying  animal." 

330.  Though  the  variety  of  expression  in  the  human  coun- 
tenance is  very  great,  it  is  ordinarily  produced  by  the  action 
of  very  few  muscles.  The  principal  muscles  are  these — the 
muscle  that  wrinkles  the  eyebrow,  causing  frowning;  the 
muscles  which  draw  down  the  corners  of  the  mouth ;  and 
those  which  draw  them  up.  When  a  smile  occurs,  it  is  pro- 
duced by  the  muscles  which  raise  the  corners  of  the  mouth. 
When  sadness  is  expressed,  it  is  done  by  the  muscles  by  which 
the  corners  of  the  mouth  are  drawn  down.  Hence  the  origin 
of  the  common  expression,  "  down  in  the  mouth."  In  laughter^ 
the  muscles  which  raise  the  corners  of  the  mouth  act  strongly, 
wrinkling  the  cheek,  simply  because  the  corner  of  the  mouth  is 
carried  up  so  far  as  to  push  up  the  cheek  before  it.  One  other 
muscle  is  brought  into  some  action — the  circular  muscle  which 
closes  the  eyelids — for  the  eyelids  are  brought  nearer  together 
in  laughter,  though  in  mere  smiling  they  are  not.  In  Fig. 
126,  representing  broad  laughter,  you  see  the  two  effects 
spoken  of  above,  the  wrinkling  of  the  upper  part  of  the  chetk, 

FIG.  126. 


THE  LANGUAGE   OF  THE   MUSCLES. 


225 


Muscles  used  in  the  expression  of  grief. 


and  the  partial  closure  of  the  eyelids.  In  weeping,  the 
muscles  that  draw  down  the  corners  of  the  mouth,  which  in 
the  mere  expression  of  sadness  act  slightly,  now  act  strongly. 
At  the  same  time  the  frowning  muscle  wrinkles  the  eyebrow. 
In  ordinary  weeping  it  does  so  but  slightly,  but  in  weeping 
from  pain  this  muscle  is  strongly  contracted.  So  it  is  also 
when  there  is  crossness  mingled  with  the  grief.  Fig.  127, 

FIG.  127. 


which  is  the  face  of  a  faun  weeping  from  pain,  illustrates  these 
points.  Sir  Charles  Bell,  from  whose  work  on  the  Anatomy 
of  Expression  most  of  the  figures  in  this  chapter  are  taken, 
says  that  he  represents  the  expression  of  weeping  in  the  face 
of  a  faun,  because  it  is  mean  and  ludicrous  as  seen  in  the 
countenance  of  man. 

331.  It  is  very  commonly  supposed  that  the  eye  has  muck 


226 


HUMAN   PHYSIOLOGY. 


Prominent  agency  of  the  mouth  in  expression. 


to  do  with  the  expression  of  the  countenance,  and  hence  such 
phrases  as  these  are  in  universal  use — a  speaking  eye ;  a  wild 
eye ;  the  witchery  of  the  eye ;  the  eye  flashed,  &c.  But  the  eye 
of  itself  has  no  active  agency  in  expression.  The  muscles 
which  move  it  have,  but  not  to  any  great  extent  ordinarily. 
Of  them  I  shall  speak  in  another  part  of  this  chapter.  The 
apparent  expression  which  the  eye  has  is  merely  apparent,  and 
not  real.  It  results  altogether  from  the  position  of  the  parts 
about  the  eye.  This  can  be  proved  to  you  by  any  portrait 
painter.  It  is  related  of  an  artist  that,  when  a  royal  visito.. 
was  admiring  a  sketch  of  the  face  of  a  weeping  child,  he  said 
to  him,  "  has  your  majesty  a  mind  to  see  how  easy  it  is  to 
make  this  very  child  laugh  ?"  As  the  king  said  that  he  should 
like  to  see  it,  the  artist  rubbed  out  a  little  at  the  corners  of  the 
mouth  and  on  the  eyebrows,  and  added  a  few  strokes  to  represent 
the  corners  of  the  mouth  as  raised,  and  the  eyebrows  as  with 
out  wrinkles,  and  the  face,  which  was  the  moment  before  the 
very  picture  of  grie£  now  exhibited  a  merry  laugh.  Afterward 
he  as  readily  restored  the  original  expression.  Now  in  this 
case  there  were  the  same  eyes  in  the  two  expressions.  The  al- 
terations were  made  only  in  the  neighboring  parts,  and  the 
same  eyes  were  apparently  weeping  eyes  at  one  time  and 
laughing  ones  at  another. 

332.  In  Fig.  128  and  129  you  can  see  how  much  the 
mouth  alone  affects  the  expression  of  the  whole  countenance. 
The  apparent  expression  of  the  eye  is  wholly  altered  by  the 


FIG.  128. 


FIG.  129. 


THE   LANGUAGE   OF   THE   MUSCLES.  227 

The  eye  has  little  active  agency  in  expression. 


change  about  the  mouth.  If  we  could  add  at  the  same  time 
a  change  at  the  eyebrows,  the  expression  of  the  eye  would  be 
much  more  affected. 

333.  The  language  which  is  ordinarily  used,  in  relation  to 
the  agency  of  the  eye  in  the  expression  of  the  countenance, 
implies  that  the  eye  itself,  apart  from  any  motion,  changes  in 
the  changing  expression.     How  this  is  done  is  not  inquired ; 
but  there  seems  to  be  an  ill  defined  notion  that  the  animal 
spirits,  as  it  is  expressed,  flow  into  the  eye  more  or  less  freely 
with  the   changing  feelings,   or   that  a   nervous  influence  is 
exerted  in  some  way  upon  the  eye,  altering  its  appearance. 
These  notions  are  so  universal,  and  are  so  inwrought  into  our 
language,  and  especially  the  language  of  poetry,  that  scientific 
men  even  are  apt  to  use  the  expressions  to  which  they  give  rise, 
in  their  descriptions  of  the  language  of  the  passions.     Even  Sir 
C.  Bell,  in  his  celebrated  book  on  the  Anatomy  of  Expression, 
in  describing  the  expression  of  the  emotion  of  joy,  uses  the 
phrase,  the  eye  is  lively  and  sparkling.     Let  me  not  be  under- 
stood to  mean,  that  I  would  have  the  expressions,  in  such  uni- 
versal use  in  common  language  and  in  poetry,  given  up.     I 
would  as  soon  claim  that  the  expression,  the  sun  rises,  should 
be  abandoned  in   common  language.     But  as  the  astronomer 
would  have  it  understood,  that  the  apparent  fact,  that  the  sun 
rises,  is  only  apparent,  not  real,  so  as  a  physiologist,  I  would 
have  it  understood,  that  the  apparent  active  agency  of  the  eye 
in  the  expression  of  the  countenance  is  not  real.     And  as  it 
would  be  objectionable  to  speak  of  the  sun  as  rising,  in  a  book 
on  astronomy,  so  in  a  professional  book  on  the  Anatomy  of 
Expression  it  is  objectionable,  in  a  description  of  the  physical 
signs  of  an  emotion,  to  use  the  common  phrases  in  regard  to 
the  agency  of  the  eye  in  expression. 

334.  Having  thus  noticed  the  principal  muscular  motions 
that  are  concerned  in  the  expression  of  the  countenance,  I  pro- 
pose now  to  go  more  extensively  into  the  subject,  and  show 
you  how  other  muscles,  besides  those  to  which  I  have  alluded, 


228  .      HUMAN   PHYSIOLOGY. 

Description  of  the  muscles  of  expression  in  the  face. 


335.  I  will  first  call  your  attention  to  the  particular  muscles 
of  expression  in  the  face,  and  indicate  their  mode  of  action. 
They  are  represented  in  Fig.  130.  There  is  a  thin  flat  muscle 


FIG.  130. 


MUSCLES    OF   THE    FACE. 

covering  the  whole  top  of  the  head,  represented  at  1,  2,  and  3 ; 
3  being  its  thin  tendinous  part.  It  is  fastened  to  the  large 
bones  behind,  and  in  front  its  fibres  end  in  the  skin  of  the  fore- 
head and  the  eyebrows,  and  in  the  circular  muscle  of  the  eye- 
lids, 4.  When  it  contracts,  therefore,  it  raises  the  skin  of  the 
forehead  and  the  eyebrows ;  and  if  it  contract  strongly,  it 
wrinkles  the  forehead.  The  circular  muscle  of  the  eyelids,  4, 
when  it  contracts  closes  the  eye.  This  and  the  large  frontal 
muscle  just  described,  you  can  see,  must  have  much  to  do  with 
the  expression  of  the  countenance.  There  is  a  very  important 
though  small  muscle  which  is  not  seen  on  this  figure.  You 
see  it  on  Fig.  113,  at  a.  It  is  attached  to  the  bone  at  the  side 
of  the  top  of  the  nose,  and  is  inserted  into  the  skin  of  the  eye- 
brow. It  is  called  the  corrugator  supercilii,  or  wrinlder  of  the 
eyebrow.  From  the  agency  which  this  muscle  has  in  the  ex- 
pression of  certain  passions  and  emotions,  comes  the  word  in 
so  common  use,  supercilious.  Though  a  little  muscle,  it  is 


THE  LANGUAGE   OF  THE  MUSCLES.  229 


Muscles  of  the  face  continued. 


truly  a  supercilious  one.  It  lias,  as  you  will  see  as  we  go  en, 
a  large  play  in  many  varieties  of  expression,  produced  by 
combinations  of  action  in  the  muscles  of  the  face.  There  are 
two  muscles  on  the  nose,  5  and  6,  which  compress  the  nose, 
and  wrinkle  its  skin.  They  have  some  agency  in  certain  ex- 
pressions of  the  countenance.  At  7  is  the  circular  muscle  of 
the  mouth.  When  this  contracts  it  closes  the  lips,  and  if  it 
act  strongly  it  pushes  them  out.  This  is  the  muscle  with  which 
in  part  pouting  is  done.  At  8  is  a  muscle  which  is  fastened 
above  to  the  bone  of  the  nose,  and  runs  down,  its  fibres  ending 
in  the  wing  of  the  nose,  and  in  the  upper  lip.  When  it  con- 
tracts, therefore,  it  moves  the  wing  of  the  nose  outward,  and 
draws  up  the  lip.  You  see  this  muscle  in  action  in  some 
emotions,  the  nostrils  appearing  spread  out.  At  9  is  a  muscle 
which  raises  the  lip,  and  at  10  and  11  are  two  muscles,  that 
raise  the  corner  of  the  mouth,  carrying  it  a  little  to  one  side. 
At  13  is  the  muscle  which  acts  in  opposition  to  the  two  last. 
It  pulls  the  corner  of  the  mouth  down.  At  12  is  the  muscle 
which  pulls  down  the  lower  lip.  At  18  is  the  muscle  in  the 
side  of  the  mouth,  which  draws  the  corner  of  the  mouth 
backward,  and  also  serves  to  press  the  cheek  inward,  and  thus 
prevent  the  food  from  getting  outside  of  the  teeth  when  we  are 
chewing  it.  This  muscle  also,  by  its  compressing  power,  forces 
out  the  air  from  the  mouth  when  the  cheeks  are  distended,  as 
in  blowing  a  horn  or  a  trumpet.  Hence  it  is  called  buccinator, 
from  buccinare,  to  blow  a  trumpet.  At  15  is  a  large  muscle 
which  closes  the  lower  jaw  against  the  upper,  and  although  its 
chief  use  is  to  masticate  the  food,  it  has  some  agency  in 
the  expression  of  the  countenance,  in  fixing  the  teeth  firmly 
together,  as  in  the  expression  of  rage.  There  are  three  muscles 
which  move  the  ear;  19,  moving  it  upward;  17,  forward; 
and  21,  backward.  These  have  but  little  power  in  man,  but 
in  some  animals  they  move  the  ear  considerably,  and  are 
prominent  agents  of  expression. 

336.  In  Fig.  131  the  muscles  about  the  mouth,  which  have 
so  much  to  do  with  the  expression  of  the  countenance,  are  very 
distinctly  showft.  At  a  is  the  muscle  which  draws  up  the  wing 
of  the  nose  and  the  lip  ;  b  raises  the  lip ;  c  raises  the  corner  of 
the  mouth ;  d  and  e  raise  the  corner  of  the  mouth,  and  at  the 
same  time  carry  it  outward ;  n  draws  it  outward  ;  m  draws  it 
downward  and  outward  in  which  it  is  assisted  by  a  broad  thin 
muscle,  o,  which  situated  just  under  the  skin  comes  up  from 
the  neck ;  I  draws  the  lower  lip  downward ;  and  i  is  the  cir- 

20 


230  HUMAJ*  PHYSIOLOGY. 

Muscles  of  expression  about  the  mouth. 


I  TW 

MUSCLES    ABOUT    THE    MOUTH. 

cular  muscle  which  closes  the  lips,  and  thrusts  them  out  in 
pouting.  At  A  is  a  short  muscle  which  is  fastened  to  the  sockets 
of  the  teeth,  and  has  its  fibres  ending  in  the  skin  of  the  chin.  It 
therefore  draws  the  chin  up  when  it  contracts.  It  has  so  much 
agency  in  the  expression  of  scorn  and  contempt  that  it  has  been 
called  the  superbus.  It  is  by  the  action  of  this  muscle,  together 
with  the  circular  muscle  i,  that  the  expression  termed  pouting 
is  produced.  The  muscles  which  I  have  thus  described  are  all 
in  pairs ;  and  in  every  pair  both  muscles  contract  always 
exactly  alike,  unless  affected  by  disease.  We  laugh  and  frown 
and  weep  on  both  sides  alike.  All  of  these  muscles  of  ex- 
pression in  the  face  are  governed  in  their  action  by  the 
branches  of  one  nerve,  the  respiratory  nerve  of  the  face. 
When  this  nerve,  therefore,  is  paralyzed  on  one  side,  and  not 
on  the  other,  as  is  no  uncommon  occurrence,  thfese  muscles  on 
the  paralyzed  side,  are  motionless,  and  the  individual  can  laugh 
and  frown  and  weep  on  only  one  side  of  the  face.  In  Fig.  82 
you  have  illustrated  the  result  of  this  partial  paralysis,  the 
face  being  perfectly  quiescent  on  the  left  side.  The  contrast 
would  have  been  still  greater  if  the  face  had  been  repre- 
sented as  in  more  decided  action,  as  laughing,  for  example. 


THE  LANGUAGE    OF   THE  MUSCLES.  231 

Action  of  particular  muscles  in  passions  and  emotions. 

337.  Having  thus  described  the  muscles  of  the  face  which 
are  the  agents  of  expression,  I  will  now  show  their  action  in  the 
expression  of  different  passions  and  emotions.     And  I  remark, 
that  you  will  see,  as  I  proceed,  that  so  far  from  there  being  any- 
one muscle  devoted  to  the  expression  of  one  emotion  or  passion, 
expression  is  commonly  the  result  of  the  combined  action  of 
many  muscles.     And  you  will  also  see  that,  by  virtue  of  this 
combination,  the  same  muscle  often  takes  a  part  in  the  ex- 
pression of  various  emotions. 

338.  When  the  frontal  muscle  (1,  2,  3,  Fig.  130)  contracts 
it  raises  the  eyebrows.     This  motion  expresses  either  doubt  or 
surprise,  and  the   observer  determines  which   it  is,  by  the  ex- 
pression of  other  parts  of  the  countenance  accompanying  it,  or 
in  other  words,  by  the  action  of  other  muscles  in  the  face. 
When  this  muscle  contracts  very  strongly,  it  draws  up  the  eye- 
brows so  much,  as  to  push  up  the  skin  of  the  forehead,  and 
wrinkle  it.     This,  as  you  will  soon  see,  is  one  of  the  many  mo- 
tions of  the  face  which  make  up  the  expression  of  great  bodily 
fear.     In  joy  this  muscle  acts  moderately,  raising  the  eyebrow, 
therefore,  but  a  little.     This  muscle  often  acts  in  connection 
with  the  corrugator  supercilii,  the  wrinkler  of  the  eyebrow. 
This  may  be  seen  in  Fig.  132,  respresenting  a  testy,  peevish, 
jealous    melancholy.      Here   the   corrugator   and   the   frontal 
muscles  are  both  in  strong  action.     You  see  also  in  this  face 
certain  muscles  about  the  mouth  acting  forcibly.     The  muscle 
which  draws  the  corner  of  the  mouth  down  is  in  action  while 
the   superbus  (A,  Fig.  131,)   is   drawing   up   the  chin  which 
pushes  up  the  lip    before   it.     At  the  same  time  the  muscle 
which  draws  up  the  wing  of  the  nose  and  the  lip,  (a,  Fig.  131,) 
contracts  to  some  extent,  producing  an   arching  of  the  mouth, 
and  a  peculiar  shape  of  the  wings  of  the  nose.     The  upper  lip 
is  arched  by  the  action  of  this  muscle  in  such  a  way,  as  to  fit 
the  arching  upward  of  the  lower  lip,  produced  by  the  superbus 
and  the  muscle  which  draws  down  the  corner  of  the  mouth. 

339.  In  the  expression  just  described,  and  illustrated  by  the 
figure,  you  see  that  the  muscle  which  draws  down  the  corner 
of  the  mouth  has.  a  considerable  agency.     Now,  this  muscle  is 
the  chief  agent  in  the  expression  of  sorrow,  as  you  saw  in  the 
first  part  of  this  chapter.     The  difference  in  the"  two  cases  lies 
in  the  combination  of  action  of  the  muscles.     Thus,  in  sorrow 
the  muscle  which  draws  down  the  corner  of  the  mouth,  does 
not  have  the  superbus  to   act  with  it,  as  in  the    case  of  the 
passion,  or  rather  compound  feeling,  represented  in  Fig.  132. 


232 


HUMAN   PHYSIOLOGY. 


Action  of  the  muscles  in  fretful  melancholy. 


FIG.  132. 


So  also,  in  some  forms  of  grief  the  corrugator  supercilii  acts 
quite  strongly,  as  seen  in  Fig.  127,  where  the  grief  is  repre- 
sented as  caused  by  bodily  pain.  It  performs  a  different  office 
in  this  case  from  what  it  does  in  the  case  of  the  expression  re- 
presented by  Fig.  132,  simply  through  the  accompanying  action 
of  other  muscles,  thus  illustrating  the  effect  of  combination  in 
muscular  action  in  varying  the  character  of  the  expression.  I 
have  already  alluded  to  the  different  degrees  of  action  in  this 
muscle  in  different  forms  of  grief  in  §  330.  In  quiet  sorrow 
this  muscle  is  not  in  action,  but  there  is  a  general  languor  re- 
laxing the  muscles  of  the  face,  while  the  corners  of  the  mouth 


THE   LANGUAGE  OF   THE  MUSCLES.  233 


Action  of  the  muscles  in  calm  pleasure,  and  in  admiration. 

are  slightly  depressed.  It  is  a  state  of  the  muscles  directly  op- 
posite to  that  which  exists  when  there  is  a  calm  quiet  pleasure. 
Then  most  of  the  muscles  are  in  a  state  of  gentle  action,  and 
the  corners  of  the  mouth  are  a  little  raised,  giving  the  radiance 
of  a  light  smile  to  the  whole  countenance.  The  frontal 
muscle,  slightly  raising  the  eyebrows,  adds  to  the  effect. 

340.  The  attitude,  for  so  we  may  call  it,  of  the  countenance 
in  admiration,  is  quite  nearly  allied  to  that  which  I  have  just 
described.     The  brow  is  expanded  by  the  action  of  the  frontal 
muscle,  and  there  is  a  slight  smile  produced  by  the  raising  of 
the  corners  of  the  mouth.     But  the  expression  differs  in  some 
respects  from  that  of  mere  pleasure.     The  frontal  muscle  acts 
rather  more  strongly  in  the  former  than  in  the  latter,  the  eye 
is  more  wide  open,  and  is  fixed  upon  the  object  of  the  admira- 
tion, and  the   mouth  is  apt  to  be  open,  the  jaw  falling  a  little, 
so  that  we  can  see  the  edge  of  the  lower  teeth  and  the  tip  of  the 
tongue.     In  both  pleasure  and  admiration  the  expression  varies 
much  in  different  individuals,  according  to  their  temperaments, 
being  characterized  by  activity  in  some,  and  in  others  more  by 
relaxation  or  even  languor. 

341.  Let* me  now  call  your  attention  to  an  expression  of  the 
countenance,  in  which  many  of  the  muscles  are  in  a  state  of 
strong  action.     I  refer  to  the  expression  of  rage  represented  in 
Fig.  133.     The  combination  of  muscular  action  here  is  quite 
extensive.     The   corrugator   super cilii   acts   forcibly,   but  un- 
steadily, as  is  the  case  with  the  action  of  all  the  muscles  in  the 
expression  of  this  passion.     The  frontal  muscle  acts  at  the  same 
time,    raising   the   eyebrows.     The    eyes   are   opened    widely, 
showing  the  rolling  eyeballs.     The  muscle  that  raises  the  upper 
lip,  6,  Fig.  131,  and  the  muscle  that  raises  the  wing  of  the 
nose  and  the  lip,  are  in  strong  action.     The  nostrils  are  there- 
fore spread  out  to  the  utmost,  arid  the  upper  lip  is  drawn  up- 
ward.    But   as   the   circular  muscle    of  the  mouth  also  acts 
strongly,   there  is   only  that  part  of  the  upper  lip  to   which 
the  muscles,  a  and  6,  Fig.  131,  are  attached,  that  can  be  drawn 
up.     This  point  is  just  where  the  sharp  eye-teeth,  or  canine 
teeth,  as  they  are  sometimes  called,  are  situated.     They  are 
therefore    seen    laid  bare.      This  allies    man  to  the  snarling 
brute,  that  shows  his  sharp  teeth  in  his  rage.     Cooke,  the  tra- 
gedian, is  said  to  have  had  great  power  in  the  use  of  these 
muscles.     "  In  him,"  says  Sir  Charles  Bell,  "  the  ringentes  (the 
snarling  muscles)  prevailed ;  and  what  determined  hate  could 
he  express,  when,  combined  with  the  oblique  cast  of  his  eyes, 

20* 


234 


HUMAN   PHYSIOLOGY. 


Complicated  muscular  action  in  expressing  riige. 


FIG.  133. 


he  drew  up  the  outer  part  of  the  upper  lip,  and  disclosed  a 
sharp  angular  tooth  !"  In  rage  the  teeth  are  firmly  closed  by 
the  muscles  which  move  the  lower  jaw,  and  when  utterance  is 
given  to  it  by  the  voice,  these  muscles  but  slightly  relax  to  let 
the  words  out  through  the  almost  closed  teeth,  and  are  rigid 
again  as  soon  as  the  words  are  finished. 

342.  The  expression  of  mere  bodily  fear,  represented  in  Fig. 
134,  is  very  different  from  that  of  rage,  although  some  of  the 
muscles  act  in  the  same  way  in  both.  The  frontal  muscle  acts 
very  forcibly,  raising  the  eyebrows  to  their  utmost  extent,  and 
the  eyeballs  are  largely  uncovered,  giving  to  the  eyes  a  broad 
stare.  The  corrugator  supercilii  is  perfectly  relaxed,  while  in 
rage  it  is  strongly  contracted.  The  lip  is  raised  and  the  nos- 
trils are  spread  out  by  the  same  muscles,  a  and  6,  Fig.  131, 
which  act  so  forcibly  in  rage.  But  the  circular  muscle  of  the 
mouth,  t,  is  relaxed,  so  that  the  whole  lip  is  raised,  instead  of 


THE  LANGUAGE  OF  THE  MUSCLES. 


235 


Movements  of  the  eye  in  expression. 


FIG.  134. 


a  part  of  it,  as  is  the  case  when  rage  is  expressed.  The  lower 
jaw  is  fallen,  while  in  rage  it  is  in  the  opposite  condition.  The 
hair  is  raised  up  by  a  general  action  of  the  whole  frontal 
muscle,  1,  2,  3,  in  Fig.  130. 

343.  The  muscles  of  the  eye,  that  is,  those  which  move  the 
eyeball  have  some  agency  in  certain  expressions  of  the  counte- 
nance. Thus,  in  admiration,  the  fixing  of  the  eye  upon  the  ad- 
mired object  makes  a  part  of  the  expression.  In  the  expression 
of  devotion  the  eye  turns  instinctively  upward.  There  are  cer- 
tain involuntary  motions  of  the  eyeball,  which  have  much  to 
do  with  expression  in  certain  states  of  the  body,  and  in  certain 
emotions.  These  motions  are  performed  by  the  oblique  mus- 
cles (§  307.)  When  the  straight  muscles  which  ordinarily  con- 
trol the  motions  of  the  eye  lose  their  power  from  a  state  of 
general  insensibility,  the  eye  is  given  over  to  the  action  of 
these  oblique  muscles,  which  are  involuntary,  and  therefore  is 


236  HUMAN  PHYSIOLOGY. 

Muscles  of  expression  peculiar  to  man. 


rolled  about  in  its  socket,  being  turned  upward  all  the  time,  so 
that  the  white  of  the  eye  only  is  seen.  This  occurs  in  sleep,  in 
fainting,  in  the  stupor  of  disease,  and  in  the  approach  of  death. 

344.  The  loss  of  power  in  the  voluntary  muscles  of  the  eyeball 
and  eyelid  is  often  seen  ludicrously  exhibited  in  the  intoxicated 
man.     He  squints  and  sees  double  from  deficiency  of  action  in 
the  straight  muscles  of  the  eyeball.     The  oblique  involuntary 
muscles  of  course  roll  the  eye  in  proportion  to  the  deficiency  of 
these  straight  muscles.     The  voluntary  muscle  too,  which  holds 
up  the  upper  lid,  fails  to  do  its  duty,  and  the  lid  is  constantly 
disposed  to  fall  over  the  eye.     The  frontal  muscle  is  therefore 
called  upon  to  aid  it.     Hence,  in  the  effort  of  the  drunkard  to 
keep  his  eyes  open,  you  see  him  raise  up  the  eyebrows,  the 
eyelids  being  of  course  dragged  up  after  them  to  a  little  extent. 
"  It  is,"  says  Sir  Charles  Bell,  "  the  struggle  of  the  drunkard  to 
resist,  with  his  half-conscious  efforts,  the  rapid  turning  up  of  the 
eye,  and  to  preserve  it  under  the  control  of   the  voluntary 
muscles,  that  makes  him  see  objects  distorted,  and  strive,  by 
arching  his  eyebrows,  to  keep  the  upper  lid  from  descending. 
The  puzzled  appearance  which  this  gives  rise  to,  along  with  the 
relaxation  of  the  lower  part  of  the  face,  and  the  slight  paralytic 
obliquity  of  the  mouth,  complete  the  degrading  expression." 

345.  I  have  thus  pointed  out  the  agency  of  the  several  mus- 
cles that  are  engaged  in  the  expression  of  the  countenance. 
Most  of  them  are  peculiar  to  man,  being  found  in  no  other 
animal.     The  inferior  animals  are  variously  endowed  in  regard 
to  muscles  of  expression.     But  even  those  that  have  the  most 
expression,  have  but  few  of  those  muscles  which  we  find  in  the 
face  of  man  devoted  to  this  purpose.     They  have  the  muscles 
that  move  the  eyes,  those  which  raise  the  upper  lip  and  thus 
expose  the  teeth,  and  to  some  extent  those  which  distend  the 
nostrils.     The  horse  is  especially  endowed  in  regard  to  this 
latter  motion.     In  that  glowing  and  beautiful  description  of  the 
horse  in  Job  it  is  said,  "  the  glory  of  his  nostrils  is  terrible." 
But  most  animals,  even  of  the  higher  orders,  have  but  a  limited 
motion  of  the  nostrils  compared  with  man.     In  him  they  have 
much  more  to  do  with  the  expression  of  the  countenance  than 
is  commonly  supposed.     Their  chief  agency  is  in  the  expression 
of  the  nobfer  passions,  and  Sir  Charles  Bell  remarks,  that  the 
great  tragedians,  Mrs.  Siddons  and  Mr.  John  Kemble,  exhibited 
their  power  in  this  respect  in  a  remarkable  manner. 

346.  None  of  the  inferior  animals  have  the  corrugator  super- 
cilii.     Indeed  they  have  no  eyebrows  to  move.     The  eyebrow 


THE  LANGUAGE  OF  THE  MUSCLES.  237 

Muscles  of  expression  in  animals. 

is  a  strong  peculiarity  of  man,  and  in  view  of  its  agency  in  the 
expression  of  the  countenance,  varied  as  it  is  by  the  frontal  mus- 
cle and  the  corrugator,  it  has  been  said  by  some  one,  that  it  is 
"  the  rainbow  of  peace,  or  the  bended  bow  of  discord."  So  also, 
the  muscles  that  raise  and  depress  the  corners  of  the  mouth 
are  wholly  peculiar  to  man.  It  is  sometimes  said  that  the  dog 
smiles.  But  if  you  observe  him  closely,  you  will  see  that  as  he 
separates  his  lips  or  opens  his  mouth,  at  the  same  time  that  he 
wags  his  tail,  there  is  no  raising  of  the  corners  of  the  mouth, 
and  therefore  no  true  smiling.  The  idea  that  he  smiles  has 
come  from  mere  association  with  other  motions  by  which  he  indi- 
cates pleasure.  The  same  can  be  said  of  the  expression  of  sorrow 
in  the  dog  and  other  animals.  There  is  little  of  it  in  the  face 
itself,  amounting  to  nothing  more  than  a  mere  downcast  look, 
if  even  that ;  and  we  connect  the  idea  of  sorrow  with  the  face, 
by  the  force  of  association,  from  hearing  the  cries  and  witness- 
ing the  movements  which  distress  produces.  The  grand  peculi- 
arities of  human  expression  are  in  the  muscles  whose  action  I 
have  noticed  in  this  paragraph,  viz.,  the  muscle  that  wrinkles  the 
eyebrow,  the  muscle  that  raises  it,  and  those  muscles  which 
move  the  corners  of  the  mouth  up  and  down.  No  animal  but 
man  can  frown,  or  weep,  or  laugh,  for  it  has  not  the  muscles  by 
which  these  acts  are  done. 

347.  Fear  and  rage  are  almost  the  only  passions  that  are 
expressed  in  the  faces  of  animals.     And  in  some  of  them  there 
are  special  provisions  in  muscular  endowment,  for  the  expression 
of  these  mere  brutal  passions,  particularly  for  rage.     Thus,  in 
beasts  of  prey  the   ringentes,  or  snarling  muscles  have  great 
power.     They  raise  the  lip  strongly,  and  display  the  sharp  long 
teeth  which  are  to  rend  their  prey  in  pieces.     The  eye  too  is 
made  terrible  by  certain  muscles  which  are  not  found  in  man. 
They  are  muscles  which  draw  the  eyelids  backward  upon  the 
prominent  eyeball,  thus  producing  a  fixed  staring  of  the  eye, 
and  exposing  its  brilliant  white  coat,  which  by  reflecting  the 
light  gives  the  eye  a  sparkling  appearance.     These  muscles  Sir 
Charles  Bell  calls  scintillantes,  from   the  apparent  scintillating 
effect  which  they  produce.     In  the  cat  tribe  light  is  reflected 
from  the  bottom  of  the  eye,  when  the  pupil  is  dilated  so  as  to 
admit  the  light  over  a  large  portion  of  the  retina.     This  occurs 
in  an  obscure   light  simply  because  the  pupil  is  then  so  much 
dilated.     The  light  is  not  created  in  the  eye,  and  it  is  no  indi- 
cation of  passion,  as  has  been  supposed. 

348.  You  have  seen  the  fact  most  fully  illustrated  in  this 


238  HUMAN   PHYSIOLOGY. 


Variety  of  combination  in  muscular  action  in  expression. 

chapter,  that  it  is  from  combinations  of  action  among  the  mus- 
cles, that  the  various  expressions  of  the  countenance  result. 
To  produce  each  one  of  these  combinations,  there  must  be  a 
consent  of  action  between  the  muscles.  Some  are  relaxed,  while 
others  are  contracted ;  and  those  which  are  contracted  are  in 
different  degrees  of  contraction.  Sometimes  this  harmony  of 
action  is  sportively  destroyed  by  one  who  has  great  command 
over  the  muscles,  of  the  face,  and  the  most  incongruous  expres- 
sions result,  mingled  together  in  the  same  countenance,  giving 
it  a  very  ludicrous  appearance.  And  I  may  remark,  that  the 
portrait  painter  is  not  always  true  to  nature,  but  sometimes  fails 
to  depict  the  full  harmony  of  muscular  action  in  the  expression 
of  the  countenance.  I  have  noticed  some  of  the  combinations 
of  muscular  action  in  expression ;  but  the  view  which  you  thus 
get  of  them  gives  you  but  a  faint  idea  of  the  infinite  variety 
of  expression  of  which  the  human  countenance  is  capable,  as  the 
result  of  these  combinations.  In  order  to  obtain  some  adequate 
idea  of  this  variety,  keeping  the  views  presented  in  this  chapter 
in  your  mind,  watch  some  one  engaged  in  speaking  or  in  conver- 
sation, in  whom  the  play  of  the  muscles  of  expression  is  peculi- 
arly free.  By  so  doing  you  will  acquire  new  views  of  the  capa- 
bilities of  the  countenance  in  communicating  thought  and  feeling, 
and  you  will  learn  a  lesson  in  this  respect  which  the  deaf  mute 
from  necessity  learns  every  day. 

349.  But  we  do  not  get  a  full  view  of  the  combination  of 
muscular  action  in  expression,  if  we  confine  our  observations  to 
the  countenance.  As  I  remarked  in  the  first  part  of  this  chap- 
ter, the  muscles  of  other  parts  of  the  body,  and  sometimes  of 
the  whole  frame,  are  brought  into  action  in  connection  with  the 
muscles  of  the  face,  in  expressing  thought  and  feeling.  The 
attitudes  and  motions  of  other  parts  of  the  body  correspond 
with  the  attitudes  and  motions  of  the  countenance,  so  as  to 
produce  an  harmonious  effect.  The  hand  is  more  used  than 
any  other  part  in  aid  of  the  countenance  in  expression ;  but  the 
whole  body  is  often  brought  more  or  less  into  action.  The 
character  of  a  passion  can  sometimes  be  inferred  from  the  atti- 
tude merely,  or  from  the  mode  of  walking,  as  you  see  one  at  a 
distance. 

"  You  may  sometimes  trace, 
A  feeling  in  each  footstep,  as  disclosed, 
By  Sallust  in  his  Cataline,  who,  chased 
By  all  the  demons  of  all  passions,  showed 
Their  work  even  by  the  way  in  which  he  trode." 


THE  LANGUAGE  OF  THE  MUSCLES.  239 

Action  of  the  respiratory  muscles  and  the  circulation  in  expression. 

350.  But  it  is  the  muscles  of  the  respiratory  organs  which 
sympathize  most  with  the  muscles  of  the  face  in  expression. 
This  sympathy  is  the  result  of  a  nervous  connection,  and  the 
nerve  of  expression  in  the  face  is  therefore,  as  before  stated, 
sometimes  called  the  respiratory  nerve  of  the  face.     Observe  the 
prominent  agency  which  the  muscles  of  the  chest  have  in  the 
decided  expression  of  the  passions  and  feelings.     In  laughing 
the  individual  draws  in  a  full  breath,  and  then   lets  it  out  in 
short  interrupted  jets,  the  muscles  of  the  throat,  neck  and  chest, 
especially  the  diaphragm,  being  convulsively  agitated.     And  if 
the  laughter  be  strong  and  continued,  he  holds  his  sides,  which 
become  really  sore,  from  the  violent  action  of  the  respiratory 
muscles  in  this  expression  of  his  emotions.     In  weeping  too, 
these  same  muscles  are  affected.     The  diaphragm  acts  spasmod- 
ically, the  breathing  is  cut  short  by  sobbing,  the  inspiration  is 
quick,  and  the  expiration  is  slow,  and  often  with  a  melancholy 
note.     But  it  is  not  alone  in  these  marked  cases  that  the  respi- 
atory  muscles  are  seen  to  act,  but  you  can  observe  their  action 
in  many  of  the  slighter  expressions  of  feeling. 

351.  There  are  certain  effects  produced  by  emotions  upon 
the  circulation,  which  heighten  the  expression  resulting  from 
muscular  action.     I  have  already  referred  to  the  blush  of  mod- 
esty, and  the  paleness  of  fear.     In  both  laughter  and  weeping 
the  spasmodic  action  of  the  muscles  of  respiration  impedes  the 
flow  of  blood  through  the  lungs ;  and  hence  the  countenance 
becomes  flushed  or  suffused  with  the  blood  of  the  impeded  cir- 
culation.    This  is  very  different  from  common  blushing,  which 
has  nothing  to  do  with  the  state  of  the  general  circulation,  but 
is  entirely  a  local  effect,  confined  to  the  capillaries  of  the  part, 
where  it  occurs.     These  capillaries  are  affected  by  the  emotion 
through  nervous  connections,  just  as  the  minute  secreting  vessels 
in  the  tear  glands  are  excited  to  unusual  action. 

352.  From  the  views  which  I  have  presented  of  the  capabil- 
ities of  the  human  countenance  in  expression,  you  must  be  as 
much  struck  with  its  adaptation  to  the  mind  that  moves  it,  as 
you  were  with  the  hand  in  this  respect.     Both  are  instruments 
of  the  mind,  by  which  it  accomplishes  its  purposes;  and  they 
would  be  out  of  place  in  any  other  animal,  even  one  of  a  higher 
order,  because  he  has  not  a  mind  capable  of  using  such  instru- 
ments to  advantage.     Man  needs  the  face,  with  all  its  endow- 
ments, to  express  his  thoughts  and  feelings,  and  the  hand  to  do 
the  handiwork  which  his  mind  designs ;  and  the  Creator  has 


240  HUMAN  PHYSIOLOGY. 

Training  of  the  muscles  of  expression.     Beauty  depends  much  on  their  action. 

proportioned  the  capabilities  of  these  instruments  to  the  necesi- 
ties  and  the  mental  powers  of  man. 

353.  As  the  muscles  of  the  face  perform  such  high  functions, 
as  the  instruments  of  the  mind  in  expression,  it  is  important 
that  they  should  be  well  trained  in  these  functions.     Much  is 
often  said  about  the  importance  of  grace  in  the  attitudes  and 
movements  of  the  body,  while  seldom  is  a  thought  given  to  the 
attitudes  and  movements  of  the  countenance.     Muscles  are  at 
work  in  the  one  case  as  well  as  in  the  other,  and  the  muscles 
of  the  face  can  be  trained  to  work  skillfully  and  gracefully  as 
well  as  the  muscles  of  any  other  part  of  the  body.     Indeed, 
grace  of  action  is  much  more  important  in  the  face  than  in  the 
body  generally,  because  the   muscles  there  are  used  so  much 
more  for  expression   than   in   any  other  part.     And  yet  the 
speaker,  who  aims  to  gesture  gracefully  with  his  arms,  is  often 
very  careless  in  regard  to  the  gestures,  for  so  we  may  call  them, 
which  are  made  by  his  face.     So  too  the  parent,  who  takes 
unwearied  pains  to  make  the  gait  and  attitudes  of  her  child  grace- 
ful, often  allows  most  uncouth  attitudes  of  countenance  to  grow 
into  a  habit.     Many  a  child  that  has  been  drilled  most  faithfully, 
in  order  to  overcome  awkwardness  of  movement,  is  suffered  to 
become  incurably  awkward  in  the  face,  as  some  one  has  aptly 
expressed  it.     Sometimes  even  a  habit  of  making  grimaces  is 
unconsciously  contracted,  which  utterly  prevents  the  countenance 
from  accompanying  the  words  that  are  uttered  with  any  thing 
like  appropriate  expression. 

354.  Beauty  depends  much  upon  the  attitudes  and  move- 
ments of  the  face,  and  not  alone  upon  the  shape  of  the  features. 
We  often  see  a  face  which  is  beautiful  in  repose,  that  becomes 
ugly  the  moment  that  it  is  in  action,  because  the  movements  of 
the  muscles  are  so  ungainly.     And,  on  the  other  hand,  we  often 
see  faces  which  are  quite  at  fault  in  the  shape  of  the  features, 
display  great  beauty  when  in  action,  from  the  movements  which 
play  so  easily  and  gracefully  among  the  muscles.     It  is  a  great 
triumph  of  the  spiritual  over  the  physical,  when  the  mind  within 
thus  puts  its  impress  of  beauty  upon  a  material  form  which  is 
destitute  of  symmetry.     When  it  does  this,  there  is  more  to 
challenge  our  admiration,  than  when  the  sculptor  chisels  the 
marble  into  beauty.     And  if  he  were  to  undertake,  in  imitation 
of  what  we  often  see  in  living  nature,  to  put  beauty  into  ill- 
shapen  features,  he  would  signally  fail.     This  can  be  done  only 
by  the  active  mind  within,  moving  plastic  features  by  the  subtle 
agency  of  nerves  and  muscles.     In  relation  to  the  inadequacy 


THE   LANGUAGE  OF  THE  MUSCLES.  241 


Skill  in  the  use  of  the  muscles  of  expression. 


of  mere  symmetry  of  form  to  meet  our  ideas  of  beauty  in  the 
living  countenance,  Addison  has  justly  said,  "No  woman  can 
be  handsome  by  the  force  of  features  alone,  any  more  than  she 
can  be  witty  only  by  the  help  of  speech." 

355.  There  is  nearly  as  much  difference  in  skill  in  the  use  of 
the  muscles  of  the  face,  as  in  the  use  of  those  of  the  hand.     And 
we  need  not  go  to  the  accomplished  orator  or  actor,  as  furnish- 
ing us  alone  with  the  higher  examples  of  this  skill.     It  is  often 
seen  exhibited  in  the  ordinary  intercourse  of  life,  in  those  who 
have  great  capacity  of  expression,  together  with  a  mind  uncom- 
monly refined  and  susceptible.     In  them  every  shade  of  thought 
and  feeling  is  clearly  and  beautifully  traced  in  the  countenance. 
While  this  is  the  result  of  education  of  the  muscles  of  expres- 
sion, an  education  of  which  the  individual  is  for  the  most  part 
unconscious,  no  direct  attempt  in  the  training  of  these  muscles 
will  succeed,  unless  the  mind  itself  be  of  the  right  character. 
Intelligence  and   kindness   cannot  be  made  to  beam  from  the 
countenance,  if  they  do  not  exist  in  the  moving  spirit  within. 
They  are  often  awkwardly  counterfeited,  the  one  by  the  bustling 
air  assumed  by  the  face  of  the  shallow  pretender,  and  the  other 
by  the  smirk  of  him  who  smiles  only  to  get  favor  or  profit  from 
others.     The  counterfeit  is  often  mistaken  for  the  reality  ;  and 
in  relation  to  the  truly  intelligent  and  kind,  there  is  often  much 
error  in  the  estimate  put  upon  their  intelligence  and  kindness, 
from  the  different  degrees  in  which  these  qualities,  when  exist- 
ing in  the  same  amounts,  are  exhibited  in  the  expression  of  the 
countenance.     In  some,  the  muscles  of  expression  respond  more 
readily  and  aptly  to  the  thought  and  feeling  within,  than  they 
do  in  others. 

356.  I  know  not  of  any  more  beautiful  and  striking  exempli- 
fication of  the  influence  of  the  mind  and  heart  upon  the  expres- 
sion of  the  countenance,  than  is  to  be  seen  in  those  institutions 
where  juvenile  outcasts  from  society  are  redeemed  from  their 
degradation  by  the  hand  of  benevolence.     You  can  often  note 
most  clearly  the  progress  of  the  mental  and  moral  cultivation 
in  the  lineaments  of  the  face,  as  lively  intelligence  takes  the 
place  of  stolid  indifference,  and  refined  sentiment  that  of  brutal 
passion.     Sometimes  a  few  weeks  suffice  to  change  the  whole 
character  of  the  expression.     The  dull  eye  becomes  bright,  not 
from  any  change  in  the  eye  itself,  but  from  the  intelligence  and 
sentiment  which  now  play  upon  the  muscles  in  its  neighborhood. 
Those  muscles  which  impart  a  lively  and  pleasant  cast  to  the 
countenance  when  they  are  in  action,  are  awakened  from  their 

21 


242  HUMAN   PHYSIOLOGY. 

The  habitual  expression  of  the  countenance  after  death. 

long  continued  dormant  state  by  the  magic  wand  of  benevolence, 
and  thus  give  outward  expression  to  the  thoughts  and  feelings, 
which  genial  influences  are  producing  in  the  mind  and  the  heart. 
.The  change  is  often  as  great  in  a  little  time,  as  it  would  be  in 
the  face  of  an  idiot,  if  he  could  be  suddenly  brought  into  the 
full  possession  of  the  mental  faculties. 

357.  The  habitual  expression  of  the  countenance,  depending 
as  it  does  upon  the  habitual  condition  of  the  muscles,  is  seen 
after  death.  In  the  state  of  relaxation  which  immediately 
ocelli's  at  death  the  face  is  very  inexpressive,  because  its  muscles 
are,  together  with  those  of  the  whole  body,  so  entirely  relaxed. 
But  very  soon  they  begin  to  contract,  and  they  assume  that 
degree  of  contraction  to  which  they  were  habituated  during 
life,  and  therefore  give  to  the  countenance  its  habitual  expres- 
sion. It  is  when  this  has  taken  place — when  the  muscles,  recov- 
ering from  the  relaxation  of  the  death-hour,  resume  their  accus- 
tomed attitude,  as  we  may  express  it,  that  the  countenance  of 
our  friends  appears  so  natural  to  us,  and  we  are  held,  as  if  by  a 
charm,  gazing  upon  the  intelligence  and  affection  beaming  there 
amid  the  awful  stillness  of  death,  till  it  seems  as  if  those  lips 
must  have  language.  And  this  expression  is  retained  through 
all  the  period  of  rigidity,  till  it  is  dissolved  by  the  relaxation 
which  succeeds-  this  state  and  ushers  in  the  process  of  decay. 
It  is  thus  that  the  soul,  as  it  takes  its  flight,  leaves  its  impress 
upon  the  noblest  part  of  its  tabernacle  of  flesh ;  and  it  is  not 
effaced  till  the  last  vestige  of  life  is  gone,  and  the  laws  of  dead 
matter  take  possession  of  the  body.  The  state  of  countenance 
which  I  have  described  is  thus  beautifully  alluded  to  by  Byron. 

He  who  hath  bent  him  o'er  the  dead, 

Ere  the  first  day  of  death  has  fled, 

The  first  dark  day  of  nothingness, 

The  last  of  danger  and  distress, 

(Before  decay's  effacing  fingers 

Have  swept  the  lines  where  beauty  lingers), 

And  mark'd  the  mild  angelic  air, 

The  rapture  of  repose  that's  there, 

The  fix'd  yet  tender  traits  that  streak 

The  languor  of  the  placid  cheek, 

And — but  for  that  s;id,  shrouded  eye, 

That  fires  not,  wins  not,  weeps  not,  now, 

And  but  for  that  chill,  changeless  brow, 

Where  cold  obstruction's  apathy 

Appals  the  gazing  mourner's  heart, 

As  if  to  him  it  could  impart 

The  doom  he  dreads  yet  dwells  upon ; 

Yes,  but  for  these,  and  these  alone, 


THE  VOICE.  243 


Superiority  of  the  vocal  apparatus  to  musical  instruments. 

Some  moments,  aye.  one  treacherous  hour, 
He  still  might  doubt  the  tyrant's  power ; 
So  fair,  so  calm,  so  softly  sealed, 
The  first,  last  look  by  death  revealed ! 


CHAPTER  XIV. 


THE  YOICE. 

358.  THE  apparatus  of  the  voice  is  truly  a  musical  instru- 
ment. We  can  see  therefore,  in  its  construction  and  arrange- 
ment, the  application  of  those  principles,  which  usually  regulate 
the  production  of  musical  sounds,  and  which  man  observes  in 
making  the  various  instruments  which  his  ingenuity  has  invented 
to  delight  the  ear.  It  is,  however,  a  much  more  perfect  instru- 
ment than  any  which  man  has  invented.  Almost  every  musical 
instrument,  it  is  true,  has  a  greater  compass  than  that  of  the 
human  voice ;  but  it  is  by  no  means  the  chief  excellence  of  an 
instrument  that  it  can  command  a  great  extent  of  the  scale. 
The  apparatus  of  the  voice  can  execute  enough  of  the  scale  for 
all  common  purposes.  It  is  wonderful  that  its  compass  is  so 
great  as  it  is,  for  it  is  a  very  small  instrument,  occupying  a  space 
of  less  than  an  inch  square  where  the  vibrating  ligaments  are 
situated.  In  every  respect  besides  compass  this  instrument  far 
excels  all  others.  Listen  to  a  good  voice  which  has  been 
well  educated.  Its  transitions  have  an  ease  and  a  grace  which 
the  workmanship  of  man  can  not  equal ;  the  richness  and  sweet- 
ness of  its  tones  are  above  all  imitation  with  the  most  perfect 
instruments ;  and  utterance  is  given  to  its  various  notes  with  so 
little  apparent  effort,  with  so  little  show  of  machinery,  in  com- 
parison with  the  instruments  made  by  man,  that  we  are  tilled 
with  wonder  at  the  effects  produced  by  so  simple,  delicate,  and 
beautiful  a  piece  of  mechanism.  But  the  most  important  cir- 
cumstance to  be  noticed  is,  that  there  are  parts  connected  with 
this  apparatus,  which  give  articulation  to  the  voice  as  it 
comes  from  the  vocal  chords,  thus  making  it  the  principal  me- 
dium of  communication  between  man  and  man.  This  distin- 
guishes it  from  every  other  musical  instrument,  and  constitutes 


244  HUMAN  PHYSIOLOGY. 


Voice  of  conversation  and  song.     Voices  of  the  brute  creation. 

its  crowning  excellence.  When  I  come  to  speak  particularly 
of  the  articulation  of  the  voice,  you  will  see  how  really  compli- 
cated is  the  apparently  simple  mechanism  that  produces  the 
varied  articulations,  and  thus  makes  the  voice  the  chief  medium 
of  mental  communication.  And  if  you  try  to  measure,  with 
the  utmost  stretch  of  conception,  the  endless  variety  of  thought 
and  feeling,  which  this  apparatus  conveys  daily,  hourly,  every 
moment  from  heart  to  heart  in  the  intercourse  of  life,  you  will 
be  able  to  estimate  in  some  good  degree  the  value  of  those  or- 
gans, which,  though  we  seldom  spend  a  thought  upon  them,  are 
so  constantly  ministering  to  our  enjoyment. 

359.  Such  being  the  high  uses  for  which  the  voice  is  designed, 
when  it  possesses  a  rich  and  flowing  melody,  and  its  articulation 
is  graceful  and  easy,  its  powers  of  fascination  are  wonderful. 
Such  a  voice  is  a  fit  medium  of  communication  for  "  thoughts 
that  breathe  and  words  that  burn."     This  is  more  often  true  of 
the  voice  of  conversation  than  that  of  song.     It  is  in  the  hourly 
intercourse  of  life  that  melody  of  voice  is  most  valuable  to  us  as 
a  source  of  enjoyment,  and  here  its  influence  is  often  astonishing. 
It  will  sometimes  give  a  charm,  not  to  say  beauty,  to  an  ordinary 
face  ;  while  on  the  other  hand,  the  fascination  of  beauty  is  often 
destroyed  by  the  utterance  of  a  voice  harsh  and  without  melody. 
And  it  may  be  remarked  that  a  rich  and  finely  modulated  voice 
of  conversation,  and  a  melodious  voice  of  song,  do  not  always 
go  together.     The  voice  which  has  delighted  the  ear  of  multi- 
tudes at  the  public  concert,  may  be  divested  of  all  its  charms, 
when  used  in  conversation ;   and  on  the  other  hand,  there  are 
many  who  sing  unskillfully,  and  yet  in  conversation  give  utter- 
ance to  genuine  and  varied  melody. 

360.  There  is  music  not  only  in  the  human  voice,  but  in  the 
voices  also  of  the  brute  creation.     And  the  varied  forms  of  the 
apparatus  by  which  it  is  produced  show  the  impress  of  the  same 
power.     What  variety  there  is  in  the  sounds  which  come  from 
the  multitudes  of  different  animals  on  our  globe,  and  how  diversi- 
fied is  the  handiwork  exhibited  in  their  vocal  organs  !     The  pow- 
er from  which  springs   this   endless  variety  is  the  same  as  that 
which  gives  such  diversity  to  the  human  countenance,  and  I 
know  riot  which  is  the  most  wonderful  display  of  it.     And  it 
may  be  remarked,  that  although  the  voices  of  some  animals  are 
harsh  and  discordant,  those  which  we  most  frequently  hear  are 
melodious.     Even  some  of  those  which  are  unpleasant  to  the 
ear,  become  in  some  degree  pleasant  when  occasionally  heard 
at  the  right  time  and  in  the  right  place,  from  the  addition  which 


THE   VOICE. 


245 


.  135. 


Two  kinds  of  wind  instruments — reed,  and  those  having  an  inflexible  mouthpiece. 

they  make  to  the  variety  of  sounds  that  we  hear,  and  from  the 
associations  which  become  connected  with  them.  A  goose  on  a 
common,  says  Cowper,  is  no  bad  performer. 

With  these  preliminary  remarks  I  proceed  to  the  investiga- 
tion of  the  subject.  I  shall  speak  first  of  the  voice  as  it  is  pro- 
duced in  the  larynx  by  the  vibration  of  the  vocal  chords  or 
ligaments,  and  then  treat  of  the  articulation  of  the  voice. 

361.  As  the  apparatus  of  the  voice  is  really  a  wind  instru- 
ment, I  will  first  develope  the  principles  on  which  wind  instru- 
ments produce  the  various  musical  notes,  and 
then  show  you  the  resemblance  between  these 
instruments  and  the  set  of  organs  which  are 
engaged  in  producing  the  notes  of  the  voice. 
Wind  instruments  are  of  two  kinds — those 
that  have  an  inflexible  mouthpiece,  and  those 
in  which  the  sounds  are  produced  by  a  vibrat- 
ing reed.  The  horn,  trombone,  trumpet,  flute, 
fife,  flageolet,  flute-stop  and  other  stops  of  the 
organ,  <fec.,  are  instruments  of  the  first  kind. 
The  cause  of  the  variation  of  notes  produced 
in  these  instruments  may  be  thus  explained. 
The  column  of  air  contained  in  the  tube  is  the 
vibrating  body  from  which  proceeds  the  sound. 
Any  thing  then  that  affects  the  column  of  air 
affects  the  note.  The  length,  the  breadth, 
and  the  mode  of  producing  the  vibrations  are 
the  causes  of  the  variation  of  the  note.  The 
holes  which  are  in  the  side  of  a  flute  are  for 
the  purpose  of  altering  the  length  of  the  con- 
fined column  of  air.  In  the  trombone  this  is 
done  by  sliding  one  part  of  the  instrument 
upon  the  other.  The  general  rule  is,  the 
longer  is  the  column  of  air  the  more  grave  is 
the  note.  Thus  in  the  flute,  the  lowest  note 
that  can  be  produced  by  the  instrument  is 
made  by  covering  all  the  holes,  so  that  you 
have  a  column  of  confined  air  the  whole  length 
of  the  tube.  The  highest  note,  on  the  other 
hand,  which  the  instrument  is  capable  of  pro- 
ducing is  made  by  so  arranging  the  fingers  as 
to  allow  the  air  to  escape  at  the  first  hole. 
In  this  case  the  length  of  the  confined  vibra- 
ting column  of  air  extends  only  from  the  mouth 


24:6  HUMAN   PHYSIOLOGY. 

Size  and  width  of  vibrating  column  of  air  affecting  the  note. 

hole  to  the  hole  from  which  the  air  escapes.  I  take  another 
illustration  from  the  organ.  Fig.  135  is  a  representation  of  one 
of  the  pipes  of  the  flute-stop  of  the  organ,  which  is  a  wooden 
box,  made  very  much  after  the  manner  of  a  boy's  chesnut 
whistle.  At  a  is  the  passage  for  the  introduction  of  the  air  ;  6 
is  the  inclosed  column  of  air,  the  vibration  of  which  produces 
the  sound ;  c  is  the  place  of  escape  for  the  air ;  and  d  is  a  mov- 
able plug,  by  means  of  which  the  vibrating  column  of  air  can 
be  made  longer  or  shorter,  according  to  the  note  desired.  In 
tuning  the  organ,  if  the  pipe  gives  too  low  a  note  the  plug  is 
moved  downward,  thus  shortening  the  column  of  inclosed  air, 
but  if  too  high  a  note,  the  plug  is  raised  up. 

362.  The  same  rule   applies  to  the  width  of  the  vibrating 
column  of  air.     The  wider  the  column  the  graver  the  note,  and 
vice  versa.     I  would  observe,  that  in  a  long,  slender  column  of 
air,  as  in  the  trombone,  by  giving  the  current  of  air  from  the 
mouth  a  great  velocity  a  high  note  may  be  produced ;   but 
where,  as  in  the  ophicleide,  the  column  is  both  wide  and  long, 
it  is  difficult  to  do  this,  because  it  is  difficult  to  produce  a  quick 
vibration  in  so  large  a  body  of  air,  with  all  the  suddenness  and 
force  with  which  we  can  move  it. 

363.  In  those  instruments  which  have  no  expedient  for  alter- 
ing the  length  of  the  column  of  air,  such  as  the  common  horn, 
the  various  notes  are  produced  by  narrowing  or  widening  the 
orifice  by  the  agency  of  the  lips,  as  the  case  requires,  at  the 
same  time  giving,  by  the  varied  velocity  with  which  the  air  is 
forced  into  the  instrument,  a  quicker  or  slower  vibration  to  the 
air.     Grave  sounds  are  produced  by  a  wide,  and  acute  by  a 
narrow  opening. .  In  playing  the  flute  the  opening  of  the  lips 
is  thus  varied  in  order  to  produce  a  vibration  which  shall  cor- 
respond with  the  length  of  the  column  of  air.     If  the  flute 
player,  with  his  fingers  arranged  for  a  high  note,  should  blow 
into  the  mouth  hole  with  his  lips  forming  a  large  orifice,  he 
would  not  produce  the  desired  note.     To  produce  the  proper 
vibration  in  a  short  column  of  air,  the  orifice  from  which  the  air 
issues  to  move  this  column  must  be  small  enough  to  corres- 
pond, and  with  it  there  must  be  the  requisite  velocity  in  the  air 
as  it  comes  from  the  mouth.     You  have  a  good  illustration  of 
the  influence  of  size  of  orifice  on  the  note  of  sound  in  common 
whistling.     The  higher  the  note  produced  the  more  narrow  is 
the  outlet  from  the  mouth.     The  size  of  it  is  regulated  by  both 
the  lips  and  the  tongue. 

364.  In  reed  instruments  the  variations  in  note  are  produced 


THE   VOICE.  247 


Reed  instruments.     Principles.     Tube  connected  with  the  reed. 


in  a  different  manner.  The  clarionet,  hautboy,  bassoon,  the 
reed  stops  in  the  organ,  &c.,  are  instruments  of  this  sort.  It  is 
the  vibration  of  the  thin  plate  called  the  reed  that  causes  the 
sound.  The  longer  this  plate  is,  the  slower  are  the  vibrations, 
and  therefore  the  graver  is  the  note,  and  vice  versa.  The  prin- 
ciple can  be  well  illustrated  in  the  reed  stops  of  the  organ.  The 
reeds  in  the  different  pipes  are  made  of  different  lengths,  accord- 
ing to  the  notes  which  they  are  to  produce.  In  a  reed  instru- 
ment played  by  the  mouth,  as  the  clarionet  for  example,  the 
rapidity  of  the  vibrations  is  regulated  by  the  pressure  of  the  lips. 
In  producing  a  high  note  the  lips  press  firmly  on  the  reed  and 
leave  but  a  small  portion  of  it  to  vibrate ;  while  in  producing  a 
low  note  the  lips  press  less  firmly  on  the  reed,  and  leave  a  large 
portion  of  it  to  vibrate. 

365.  You  see  that  the  same  principles  apply  to  the  reed  as 
to  the  column  of  air  in  the  other  kind  of  wind  instruments.     In 
both  cases  the  longer  and  thicker  the  vibrating  body  the  coarser 
is  the  vibration,  and  the  graver  the  note.     This  same  principle 
also  applies  to  stringed  instruments.     Thus  in  the  piano,  the 
grave  notes  come  from  long  and  large  strings,  while  the  higher 
notes  come  from   slender  and  short  ones.     In  the  violin  the 
strings  are  all  of  the  same  length,  the  larger  strings  giving  the 
graver  notes,  and  the  smaller  the  higher  ones.     The  notes  are 
varied  also  in  the  case  of  each  string,  by  varying  the  tension. 
They  are  varied  too  while  playing  on  the  instrument  by  varying 
the  length  of  the  vibrating  strings  by  the  pressure  of  the  fingers. 

366.  The  reed  is  always  connected  with  a  »tube.     Has  this 
any  influence  upon  the  note  produced  by  the  reed  ?     It  contains 
a  column  of  air  through  which  the  sound  caused  by  the  vibra- 
tion of  the  reed  must  pass.     Unless,  then,  the  vibration  of  this 
column  of  air  corresponds  with  the  vibration  oF  the  reed,  it  will 
alter  the  note.     It  does  alter  the  note  to  some  extent  always. 
It  never  raises  it,  but  always  makes  it  more  grave.     That  is, 
the  vibration,  in  passing  from  the   reed  to  the  column  of  air, 
becomes  less  rapid  and  coarser,  as  is  always  the  case  when  vi- 
bration passes  from  any  substance  to  another.     But  the  tube  is 
so  arranged  that  there  may  be  as  little  change  in  this  respect 
as  possible,  and  yet  have  the  combined  effect  of  a  reed  and  wind 
instrument  secured.     Holes  are  therefore  properly  placed  in  the 
side  of  the  tube,  so  that  with  the  fingers  the  column  of  confined 
air  may,  in  the  case  of  every  note,  be  placed  in  correspondence 
with  the  vibration  of  the  reed.     Suppose  the  tube  to  be  long 
and  without  holes ;  in  this  case  low  notes  could  be  easily  pro- 


248  HUMAN   PHYSIOLOGY. 

Description  of  the  organ  of  the  voice.     Hyoid  bone.     Lnrynx.    Trachea. 

duced,  but  attempt  a  high  note  arid  you  would  fail.  The  reason 
is  obvious.  The  low  note  is  caused  by  a  low  and  coarse  vibra- 
tion of  the  reed,  for  the  transmission  of  which  a  long  column 
of  air  is  fitted.  But  if  a  high  note  be  attempted,  the  slow 
vibration  of  the  long  column  of  air  disagrees  with  the  quick 
vibration  of  the  reed,  and  flattens  very  much  the  sound  after  it 
comes  from  the  reed,  as  it  passes  through  the  tube.  As  I  have 
already  hinted,  the  object  of  the  tube  is  to  secure  in  the  instru- 
ment the  combined  effect  of  a  reed  and  a  wind  instrument. 
The  tube  makes  the  reed  speak,  as  it  is  expressed ;  that  is,  it 
gives  intensity  and  an  agreeable  character  to  the  sound.  If 
you  disconnect  the  reed  of  the  hautboy  or  bassoon,  for  example, 
from  its  tube,  and  blow  upon  it,  you  can  produce  all  the  variety 
of  notes,  but  the  sound  is  disagreeable ;  but  by  connecting  the 
tube  with  the  reed  you  produce  a  compound  sound,  as  we  may 
call  it,  which  has  a  sweet  and  rich  melody. 

We  will  now  examine  the  apparatus  of  the  voice,  and  see  how 
far  the  principles  which  I  have  developed  in  relation  to  common 
musical  instruments  are  applicable  to  this  instrument. 

367.  Just  at  the  root  of  the  tongue,  as  described  in  the  Chap- 
ter on  the  Bones,  §  282,  is  a  small  bone,  shaped  so  much  like 
the  Greek  letter  v  that  it  is  called  the  hyoid  or  U-like  bone. 
The  round  end  of  this  bone  is  towards  the  root  of  the  tongue, 
and  its  two  ends  point  backward  toward  the  pharynx.  To 
this  bone  is  connected  a  long  cartilaginous  tube  extending  to 
the  lungs,  called  the  trachea,  or  windpipe.  It  is  through  this 
tube,  as  you  have  already  learned,  that  the  air  goes  back  and 
forth  from  the  lungs  in  respiration  and  speech.  It  is  not  one 
solid  tube,  but  is  composed  of  a  great  number  of  rings  of  carti- 
lage connected  together  by  membranous  parts.  The  rings  are 
not  perfect  circles.  They  are  deficient  behind,  and  this  deficiency 
is  supplied  by  a  membrane.  The  object  of  this  arrangement  is 
evident.  The  part  of  the  tube  where  the  rings  are  deficient  is 
Jirectly  in  front  in  its  whole  length  of  the  oesophagus  or  gullet, 
the  tube  through  which  the  food  passes.  If  the  rings  had  been 
made  entire,  it  is  manifest  that  their  pressure  would  interfere 
somewhat  with  swallowing.  But  it  is  the  upper  part  of  the 
windpipe,  that  part  which  is  immediately  below  the  U-like  bone, 
rtrhich  claims  our  attention  as  the  seat  of  the  formation  of  the 
voice.  This  part  is  called  the  larnyx.  It  is  formed  of  five  car- 
tilages, the  arrangement  of  which  I  will  now  show  you.  The 
largest  of  these  cartilages,  the  one  which  forms  the  most  of  the 
body  of  this  music-box,  as  we  may  call  it,  is  the  thyroid.  It  is 


THE  VOICE. 


249 


Thyroid,  cricoid  and  arytenoid  curtilages. 


the  pomum  Adami,  or  Adam's  apple,  which  is  so  easily  felt  in 
the  top  of  the  neck.  This  cartilage  forms  the  front  and  sides 
of  the  larynx,  but  it  is  open  behind.  The  cricoid  cartilage  is 
shaped  very  much  like  a  seal  ring,  and  this  resemblance  gives 
it  its  name.  The  narrow  part  of  it  is  situated  directly  under 
the  thyroid  cartilage,  in  its  front  and  at  its  sides,  but  the  broad, 
seal-like  part  of  it. is  behind,  projecting  upward  and  filling  up  a 
part  of  the  open  space  left  by  the  deficiency  of  the  thyroid  in 
in  its  rear.  A  side  view  of  these  parts 
is  given  in  Fig.  136,  in  which  1  is  the  FIG  136> 

the  U-like  bone ;  4  is  the  thyroid  car- 
tilage; and  6  the  cricoid.  At  8  is 
the  back  part  of  the  cricoid,  filling  up 
a  part  of  the  space  in  the  open  rear 
of  the  thyroid ;  3  is  a  horn  shaped 
projection  of  the  thyroid,  and  5  is  a 
smaller  one  below,  projecting  over  on 
to  the  outside  of  the  cricoid ;  2  is  a 
strong  membrane  or  ligament  connect- 
ing the  hyoid  or  U-like  bone  with 
the  top  of  the  thyroid  ;  9  is  the  epi- 
glottis, drawn  up  by  a  hook  ;  and  at 
V  are  the  rings  of, the  trachea.  The 
epiglottis  is  composed  in  part  of  car- 
tilage. It  is,  as  I  have  already  told 
you,  in  the  Chapter  on  Digestion,  §  78, 
the  lid  of  the  music  box,  the  larynx, 
shutting  down  when  we  swallow,  so  side  view  of 

that  the  food  or  drink  may  pass  over  THE  LARYNX. 

it,  and  being  raised  up  when  we 
breathe  or  speak. 

368.  There  are  two  small  cartilages  which  are  not  seen  in 
this  figure,  called  arytenoid  cartilages,  from  two  Greek  words, 
meaning  ladle  and  shape,  because  they  bear  some  resemblance 
in  form  to  a  ladle.  They  stand  in  the  open  space  in  the  rear 
part  of  the  thyroid,  on  the  top  of  the  cricoid  cartilage.  They 
are  the  pillars  to  which  the  vocal  chords  or  ligaments  are  attached 
behind.  These  two  cartilages  are  movable,  having  a  regular 
joint  with  the  upper  edge  of  the  cricoid.  There  are  small  mus- 
cles which  pull  them  in  different  directions,  and  thus  change 
the  degree  of  tension  and  the  position  of  the  vocal  ligaments, 
and  of  course  vary  the  note  of  the  sound  produced  by  their  vibra- 
tion. That  you  may  understand  how  this  is  done,  I  give  you 


250 


HUMAN  PHYSIOLOGY. 


Vocal  ligaments.     Mode  of  their  action. 


Diagram  showing  the  action  of  the 
VOCAL    LIGAMENTS. 


FIG.  138. 


in  Fig.  137  a  diagram  showing  the  arrangement  of  these  liga- 
ments. It  represents  a  view  of  them  as  you  look  down  into 
the  larynx,  in  which  a  is  the  front  of  the  thyroid  cartilage,  and  bb 
are  the  two  arytenoid  cartilages.  To 
these  you  see  are  attached  two  sheets 
of  membrane,  which  are  also  fastened 
all  around  to  the  inside  of  the  thy- 
roid. If  these  movable  posts,  as  we 
may  call  them,  to  which  the  ligaments 
are  thus  attached,  be  drawn  back- 
ward, it  is  obvious  that  it  will  make 
the  ligaments  more  tense.  If  they 
are  separated  from  each  other,  the 
opening  between  the  ligaments  will 
be  widened.  If  they  are  brought 
nearer  together,  this  opening  will  be 
narrowed,  and  the  forward  part  of  the  free  edge  of  each  liga- 
ment will  be  prevented  from  vibrating,  because  it  is  here  brought 
in  contact  with  the  other  ligament. 
Now  there  are  small  muscles  which 
are  attached  to  the  arytenoid  car- 
tilages for  the  purpose  of  moving 
them  as  I  have  pointed  out.  The 
figure  which  I  have  presented  is  a 
mere  diagram,  to  show  the  arrange- 
ment of  the  ligaments  for  the  pro- 
duction of  the  various  notes  of  the 
voice.  In  Fig.  138  is  represented 
the  actual  appearance  of  the  liga- 
ments and  the  arytenoid  cartilages, 
as  you  look  down  upon  them.  The 
ligaments  you  observe  are  thicker  at 
their  free  edges  than  any  where  else. 

369.  In  Fig.  139  you  have  a  view  of  the  larynx  and  trachea 
irom  behind,  in  which  are  shown  two  of  the  muscles  that  move 
the  arytenoid  cartilages.  At  h  is  the  hyoid  bone ;  t  t,  the 
posterior  margins  of  the  thyroid  cartilage;  between  these 
stands  the  broad  rear  part  of  the  cricoid  cartilage,  the 
middle  line  of  which  you  see  at  c;  at  r  are  the  rear  ends 
of  the  rings  of  the  trachea  ;  I  is  the  membranous  part  of  the 
trachea,  which  lies  in  front  of  the  oesophagus  or  gullet;  a 
marks  the  top  of  one  of  the  arytenoid  cartilages,  and  you  see 
also  the  top  of  the  other ;  e  is  the  epiglottis  represented  as 


THE  VOCAL  LIGAMENTS. 


THE  VOICE. 


251 


Muscles  regulating  the  tension  of  the  vocal  ligaments. 


FIG.  139 


BEAR  VIEW  OF  THE  LARYNX  AND  THE  TRACHEA. 


raised  up  as  when  we  are  speaking  ;  b  is  a  muscle,  which,  be- 
ginning at  the  middle  line  of  the  cricoid  cartilage,  runs  forward, 
and  is  fastened  to  the  outside  of  the  arytenoid  cartilage,  there 
being  one  like  it  on  the  other  side,  as  you  see  ;  s  is  another 
muscle  going  from  the  cricoid  to  the  arytenoid  cartilage,  which 
also  has  its  fellow  on  the  other  side.  You  can  see  that  the  muscle, 
s,  and  its  fellow,  if  contracted  would  bring  the  arytenoid  cartilages 
nearer  together,  and  so  diminish  the  opening  between  the  vocal 
membranes  which  are  fastened  to  these  pillars.  The  muscle,  6, 
and  its  fellow,  on  the  other  hand,  when  they  act,  so  draw  upon 
the  outer  edges  of  the  arytenoid  cartilages  as  to  separate  these 
cartilages  from  each  other,  and  therefore  enlarge  the  openings 
between  the  ligaments.  There  are  other  muscles  not  seen  in 
the  figure,  that  alter  the  size  of  the  orifice  between  the  vocal 
ligaments  and  their  degree  of  tension,  and  thus  affect  the  notes 
of  the  voice. 

370.  I  have  described  the  true  vocal  ligaments.     But  there 


252 


HUMAN   PHYSIOLOGY. 


Interior  view  of  the  larynx  and  epiglottis. 


is  another  pair  of  ligaments  directly  above  them,  the  space 
between  which  is  the  real  opening  into  the  larynx,  upon  which 
the  epiglottis  shuts  down  when  we  swallow.  You  will  get  a 
good  idea  of  the  arrangement  of  the  two  pairs  of  ligaments  from 
Fig.  140.  This  is  a  representation  of  an  inner  view  of  one 


FIG.  140. 


INTERIOR    OF    THE    LARYNX. 

half  of  the  larynx,  the  division  being  made  directly  down,  and 
from  front  to  rear.  At  t  is  the  front  of  the  thyroid  cartilage 
with  its  cut  edge ;  at  c  c,  are  the  two  cut  edges  of  the  cricoid, 
showing  how  narrow  is  its  front  part  compared  with  its  broad 
rear  portion  ;  a  is  the  left  arytenoid  cartilage,  c  showing  the 
place  where  it  is  united  by  a  joint  to  the  top  of  the  cricoid ;  /  is 
the  trachea ;  r  is  the  true  vocal  ligament  or  chord ;  v  is  the 
space  between  this  and  the  upper  ligament ;  and  e  is  the  epig- 
lottis which  is  shut  down  upon  the  upper  ligaments  as  a  cover 
by  the  contraction  of  the  muscle  6,  just  when  this  is  needed. 


THE   VOICE. 


253 


Upper  and  lower  ligaments.     The  lower  the  true  vocal  chords. 


FIG.  141. 


In  Fig.  141  is  a  diagram  represent- 
ing the  plan  of  these  two  pairs  of 
ligaments,  as  shown  by  a  perpendic- 
ular section  from  side  to  side.  B  B 
represents  the  vocal  ligaments,  C  C 
the  upper  ligaments,  and  V  V,  the 
two  recesses  between  them. 

371.  We   know   that   it   is   the 
lower  ligaments  that  are  the  true 
vocal   chords,     because   the     parts 
above  these,  even  the  upper  liga- 
ments, may  be  all  cut  away,  and  yet 
a   vocal  sound  may  be  produced  ; 
while  if  an  opening  be  made  into 
the  larynx   below   the   lower   liga- 
ments the  voice  will  be  destroyed. 
Magendie,    a    French    physiologist, 
speaks  of  a  man,  who  on  account  of 
an  opening  in  the  larynx  was  never 
able  to  speak  without  pressing  his 
cravat  tightly  against  this  opening, 

in  order  to  prevent  the  air  from  escaping  through  it.  Many 
experiments  have  been  tried  with  the  larynx  after  death  to 
verify  the  results  above  stated.  The  lower  ligaments  are  then 
the  vocal  chords,  by  the  vibration  of  which  all  the  different 
notes  of  the  voice  are  produced.  And  the  other  parts  of  the 
vocal  apparatus  serve  only  to  modify  the  sound  caused  by  the 
ligaments.  The  lungs  act  merely  as  the  "  wind-chest,"  to  hold 
the  air  which  being  forced  out  strikes  on  the  ligaments,  and 
makes  them  to  vibrate. 

372.  Let  us   now    apply  to   this    apparatus   the    principles 
which  I  have  developed  in  the   beginning  of  this  chapter,  as 
regulating  the  variation    of  note  in  common  musical  instru- 
ments.    The  size  of  the  aperture,  through  which  the  sound  is 
thrown  out,  influences  the  note,  of  which  we  have  a  familiar 
example  in  whistling.     And  as  you  have  seen  that  the  size  of 
the   opening  between   the  vocal   ligaments  is    varied  by   the 
muscles  moving  the  arytenoid  cartilages,  this  must  have   an 
influence  upon  the  note  of  the  voice.     But  this  is  not  the  only 
cause  of  the  variation  of  the  note.     As  I  showed  in  relation  to 
the  reed,  and  to  the  strings  of  stringed  instruments,  so  also 
here  the  larger  and  less  tense  are  the  vibrating  bodies,  the  vocal 
chords,  the  graver  is  the  note,  and  vice  versa.     You  have  seen 

22 


254  HUMAN   PHYSIOLOGY. 

Principles  of  musical  instruments  applied  to  the  vocal  apparatus. 

how  these  chords  or  ligaments  are  varied  in  tension  by  the 
action  of  the  muscles  that  move  the  arytenoid  cartilages.  You 
have  also  seen  that,  as  these  cartilages  are  brought  near  to- 
gether by  the  muscles,  the  extent  of  the  free  vibrating  edges  of 
the  ligaments  is  shortened,  because  their  edges  are  brought  to- 
gether in  their  anterior  part  (Fig.  137).  Magendie  verified 
this  by  observation.  He  opened  the  throat  of  a  noisy  dog  in 
such  a  way  that  he  could  look  directly  upon  the  vocal  ligaments. 
When  the  sounds  were  grave,  he  observed  that  the  ligaments 
vibrated  in  their  whole  length,  and  that  the  air  passed  out  in  the 
whole  length  of  the  chink  between  them.  But  when  the 
sounds  were  on  a  high  note,  the  ligaments  did  not  vibrate  in 
their  anterior  part,  but  only  in  the  posterior,  and  the  air  passed 
out  only  at  the  open  vibrating  part.  It  is  manifest  that  in  pro- 
ducing the  various  notes,  the  muscles  that  move  the  arytenoid 
cartilages  act  upon  the  ligaments  just  as  the  lips  do  upon  the 
reed  of  the  hautboy  or  bassoon,  regulating  the  extent  and  the 
rapidity  of  the  vibrations. 

373.  There  has  been  much  discussion  as  to  the  kind  of 
musical  instrument  the  larynx  most  resembles.     From  the  facts 
above  stated  it  appears  clear  that  it  most  resembles  reed  instru- 
ments, though  its  analogy  to  stringed  instruments  is  also  quite 
apparent.     There  is  also  a  resemblance  to  some  small  extent  to 
common  wind  instruments,  as  the  size  of  the  orifice  between  the 
vocal   ligaments    must   have   some   influence   upon  the   note. 
Whatever  we    may  think   as  to  the   degrees  in  which  these 
analogies  exist,  we  can  see  that  the  great  principle  of  musical 
sounds  is  regarded  in  all  the  arrangements  of  the  vocal  appara- 
tus, viz.,  that  coarse  and  slow  vibrations  produce  grave  notes, 
while  rapid  and  fine  vibrations  produce  high  ones. 

374.  I  will  trace  the  resemblance  between  the  instrument  of 
the  voice  and  common  musical  instruments  still  farther.     The 
sound  as  it  comes  from  the  larynx  passes  through  a  tube,  just 
as  the  sound  coming  from  a  reed  does  in  a  reed  instrument. 
In  other  words  there  is  a  body  of  inclosed  air  extending  from 
the  larynx  to  the  outlets  of  the  mouth  and  nose,  which  vibrates 
in  transmitting  the  sound  from  the  larynx.     This  body  of  air  is 
not  as  simple  in  its  form  as  that  is  which  is  inclosed  in  the  tube 
of  common  reed  instruments.     It  has  three  outlets,  the  mouth 
and  the  two  nostrils.     The  sound  of  the  voice,  however,  seldom 
comes  out  from  the  orifices  of  the  nostrils,  but  almost  always 
from  the  mouth.     In  humming  it  comes  altogether  from  the 
nostrils.     In  ordinary  speaking  and  singing  the  cavities  of  the 


THE   VOICE.  255 


Tube  of  the  vocal  apparatus  like  that  of  a  reed  instrument. 

nose  act  as  reverberating  cavities,  the  sound  which  reverberates 
there  issuing  from  the  mouth.  This  fact  will  be  illustrated 
when  I  come  to  speak  of  the  articulation  of  the  voice.  The 
curtain  of  the  palate  answers  as  a  sort  of  swing  door  between 
the  cavity  of  the  mouth,  and  the  cavities  of  the  nose,  to  direct 
the  air  the  one  way  or  the  other.  When  a  sound  is  to  be 
reverberated  in  the  cavities  of  the  nose,  it  hangs  in  such  a  way 
that  the  communication  between  the  mouth  and  these  cavities 
is  open. 

375.  You  have  seen  that  the  tube  connected  with  the  reed 
in  the  reed  instrument  is  so  arranged,  that  the  length  of  the 
confined   column    of  air   can    be    changed,  in    producing  the 
different  notes,  the  vibration  of  the  air  thus  being  brought  into 
correspondence  with  that  of  the  reed.     How  is  the  same  thing 
effected   in    the  vocal    apparatus  ?     It  is   done  in   two  ways. 
First,  the  length  of  the  tube  is  altered.     If  you  place  your 
finger  on  the  front  of  the  larynx,  and  then  sound  various  notes, 
you  will  feel  the  larynx  rise  when  you  sound  a  high  note,  and 
fall  when  you  sound   a  grave   one.     The  object  of  this  move- 
ment is  to  alter  the  distance  from  the  larynx  to  the  outlet  of  the 
mouth,  in  other  words,  to  alter  the  length  of  the  column  of  air 
in  the  tube,  so  that  it  may  correspond  in  its  vibration  with  the 
vibration  of  the  vocal  chords.     But  the  size  of  this  column  of 
air  is  altered  in  another  way.     It  is  altered  in  its  width,  which, 
as  I  have  remarked  in  relation  to  musical  instruments,  §  362,  is 
quite  as  effectual  in  changing  the  vibration  as  an  alteration  of 
length.     The  tube  of  the  vocal  instrument  you  readily  see  can 
be   altered  in   its  width  by  the    muscles  of  the   throat  and 
mouth. 

376.  The  object  of  the  tube  of  the  reed  instrument  is,  I  have 
stated  in  §  366,  to  make  the  reed  speak,  as  it  is  termed  ;  that  is, 
to  give  intensity  and  an  agreeable  character  to  the  sound.     The 
tube  in  the  instrument  of  the  voice  undoubtedly  does  the  same 
thing.     If  the  voice  should  come  directly  from  the  larynx  with- 
out passing  through  the  tube  attached  to  it,  it  would  be  as  dis- 
agreeable as  the  sound  of  a  reed  when  separated  from  its  tube. 
The   voice  gets  most  of  its  melody  after  it   is  made   in  the 
larynx,  as  it  passes  out  through  the  column  of  air  in  the  throat 
and  mouth.     And  it  is  the  variations  of  this  tube  produced  by 
the  muscles   that  surround  it  that  give  to  the  voice  its  variety 
of  tone  as   well  as  its  melody,  thus  constituting  one  of  the 
great  excellencies  of  the  vocal  instrument  in  comparison  with 
all  common  musical  instruments.     If  the  voice  of  Jenny  Lind 


256  HUMAN  PHYSIOLOGY. 

•  '         — — — — — — ' •  * 

Seat  of  hoarseness.     Influence  of  the  epiglottis  on  the  voice. 

could  be  made  to  come  directly  from  the  larynx,  notwithstand- 
ing its  great  compass,  it  would  lose  all  its  charm,  and  would  be 
better  fitted  for  the  performances  of  Punch  and  Judy,  than  for 
the  public  concert. 

377.  It  is  a  very  common  popular  notion,  that  a  hoarseness, 
or  a  loss  of  voice,  indicates  disease  in  the  lungs.     But  y6u  have 
seen  that  the  lungs  are  the  mere  bellows,  or  the  "  wind-chest "  of 
the  organ  of  the  voice,  and  that  the  voice  is  produced  by  the  vi- 
bration of  the  vocal  ligaments  as  the  air  forced  from  the  wind- 
chest  strikes  them,  and  is  modified  by  the  tube  which  extends 
from  the  larynx  to  the  outlet  of  the  mouth.     Any  alteration  of 
the  sound  therefore,  as  hoarseness,  must  be  caused  by  difficulty 
either  in  the  ligaments,  or  the  tube,  or  in  both,  and  an  en- 
tire loss  of  the  voice  can  be  caused  only  by  an  affection  of  the 
ligaments.     Disease  in  the  lungs,  it  is  true,  is  very  apt  to  affect 
the  larynx  and  the  throat  by  extension  or  by  sympathy,  and 
thus  alter  the  voice  ;  but  it  often  does  not.     Consumptive  per- 
sons sometimes  have  a  clear  voice  almost  to  the  last. 

378.  The  epiglottis,  besides  acting  as  a  lid  for  the  larynx,  for 
the  food  to  pass  over  it  into  the  oesophagus,  also  has  an  in- 
fluence upon  the  voice  in  two  ways.     First  it  can  be  made  to 
narrow  more  or  less  the  passage  of  air  from  the  larynx.     And 
secondly,  some  experiments  of  M.  Grenie  on  reed  instruments 
show,  that  it  has  an  influence  upon  the  intensity  of  the  voice. 
When  experimenting  on  some  reed  instrument,  he  wished  to  in- 
crease the  intensity  of  sound  without  changing  the  reed.     For 
this  purpose  he  gradually  increased  the  force  of  the  current  of 
the  air ;  but  this  not  only  augmented  the  sound,  but  raised  its 
note.     He  at  length  obviated  the  difficulty,  by  placing  obliquely 
in  the  tube,  just  under  the  reed,  a  supple  elastic  tongue.     He 
could  now  give  greater  intensity  to  the  sound  without  raising 
its  note.     The  epiglottis  seems  to  perform  the  same  office  in 
our  vocal  tube,  for  it  is  elastic  and  supple  like  the  little  tongue 
which  M.  Grenie   placed  in  the  tube  of  his  instrument.     Its 
situation  is  similar  also,  it  being  directly  over  the  double  reed 
of  the  larynx,  as  we  may  call  its  ligaments.     There  are  muscles 
to  move  it,  so  that  it  maybe  at  the  right  inclination  in  all 
cases.     One  of  these  is  seen  in  Fig.  140  at  b. 

379.  I  have  thus  traced  the  analogy  between  the  apparatus 
of  the  human  voice,  and  musical  instruments.     How  nicely  ad- 
justed are  all  its  parts !     With  what  precision  must  the  muscles 
that  move  them  act  in  those  who  are  able  to  produce  the  most 
delicate,  as  well  as  the  most  striking  variations  of  note  !     Every 


THE  VOICE.  257 


Delicucy  of  the  action  of  the  vocal  muscles.    Gliding  from  note  to  note. 

modulation  of  the  voice,  however  slight,  requires  muscular  ac- 
tion to  effect  it.  The  vocal  ligaments  must  be  put  in  just  such 
a  state,  or  the  wrong  sound  will  be  produced.  So  too,  the 
muscles  of  the  mouth  and  throat  must  put  the  tube  of  the 
vocal  instrument  into  the  right  shape,  in  order  to  have  the  con- 
tained column  of  air  correspond  in  vibration  with  the  vocal 
ligaments.  To  have  some  conception  of  the  variety  of  the 
motions  of  the  muscles  concerned  in  the  modulation  of  the 
voice,  listen  to  some  singer  whose  voice  can  command  with  ease 
and  freedom  a  great  extent  of  the  scale.  For  every  note  that 
you  hear  there  is  a  distinct  and  particular  adjustment  of  the 
vocal  ligaments,  and  of  course  a  particular  degree  of  contrac- 
tion of  the  little  muscles  that  move  them.  Let  us  see  how  deli- 
cate the  action  of  these  parts  is.  U  is  calculated  that  the  liga- 
ments vary  in  length  only  about  the  •£  of  an  inch  in  producing 
all  the  notes  of  the  voice.  Now  the  natural  compass  of  the 
voice  (that  is  its  range  from  its  lowest  to  its  highest  note)  in 
most  singers  is  about  two  octaves  or  24  semitones.  Within 
each  semitone  a  singer  of  ordinary  capability  can  produce  5  or 
6  distinct  notes ;  so  that  for  the  whole  number  of  notes  that  he 
can  sound  distinctly  120  is  a  moderate  estimate.  He  therefore 
produces  120  different  states  of  tension  in  the  vocal  ligaments. 
Arid  as  the  variation  in  their  length  for  passing  from  the  lowest 
of  these  120  notes  to  the  highest  is  only  the  -J-th  of  an  inch,  the 
variation  required  to  pass  from  one  note  to  another  will  be  only 
the  -rJrrth  of  an  inch.  A  very  expert  singer  can  produce  a 
much  more  delicate  action  than  this,  and  distinctly  appreciate 
the  result  by  his  ear.  How  great  the  contrast  between  «the 
minute  contractions  of  the  little  muscles  that  move  these  vocal 
ligaments,  and  the  contractions  of  the  large  muscles  in  the  arm 
that  wield  the  ax  and  the  sledge-hammer! 

380.  It  is  proper  to  notice  here  one  very  marked  difference  be- 
tween the  vocal  apparatus  and  common  musical  instruments.  I 
have  spoken  in  the  previous  paragraph  of  distinct  notes  as  exe- 
cuted by  the  voice.  Most  instruments  execute  only  these  distinct 
notes.  But  the  voice  can  also  glide  from  one  note  to  another 
with  a  continuous  sound.  In  this  respect  the  vocal  instrument 
is  superior  to  common  musical  instruments.  There  is  one 
instrument,  however,  the  violin,  in  which  this  gliding  movement 
can  be  to  a  great  extent  imitated.  It  is  done  by  sliding  the 
finger  on  the  string,  as  it  vibrates  under  the  bow.  A  peculiar 
use  of  this  gliding  movement  distinguishes  tjie  voice  of  speech 
from  that  of  song,  as  I  shall  show  you  in  another  part  of  this 

22* 


258  HUMAN   PHYSIOLOGY. 


Training  of  the  muscles  of  the  voice.    Importance  of  keeping  the  chest  full  of  air. 

chapter.  It  is  by  an  imitation  of  this,  by  sliding  the  finger  on 
the  string,  that  the  violin  can  be  made  to  imitate  so  well  the 
tones  of  conversation. 

381.  The  muscles,  by  which  all  the  variations  in  the  tension  of 
the  vocal  ligaments  are  effected,  receive  nerves  from  the  brain,  and 
are  under  the  guidance  of  the  will.     When  the  mind  therefore 
wills  to  produce   a  certain  sound,  these  muscles  immediately 
place  the  parts  in  such  a  state  as  to  cause  that  sound.     This  is 
true  of  the  muscles  that  put  the  tube  in  correspondence  with 
the  larynx,  as  well  as  of  those  which  produce  the  right  state  of 
tension  in  the  ligaments.     It  is  also  true  of  the  muscles  which 
articulate  the  voice,  of  which  I  am  yet  to  speak,  and  of  those 
which  work  the  chest,  the  bellows  or  "wind-chest"  of  the  organ 
of  the  voice.     The  muscles  of  this  apparatus  are  in  the  same  con- 
dition with  other  voluntary  muscles;  and  therefore,  like  them, 
the  more  they  are  trained  in  the  exercise  of  their  powers,  the 
more  perfect  will  be  their  action.     The  muscles  in  the  arm  and 
hand  of  the  infant  learn  to  execute  the  motions  of  which  they 
are  capable  gradually.     Just  so  it  is  with  the  muscles  of  the 
voice — from  our  infancy  they  are  trained  under  the  ear  as  an 
instructor.     The  muscles  which  regulate  the  adjustment  of  the 
vocal  ligaments,  in  producing  the  different  notes,  cannot  do  it 
accurately  without  the  education  of  exercise,  any  more  than  the 
lips  of  one  just  beginning  to  play  on  the  hautboy  or  clarionet, 
can  regulate  their  pressure  on  the  reed,  so  as  to  sound  the  dif- 
ferent notes  correctly.     The  analogy  is  perfect,  for  it  is   the 
muscles  moving  the  vocal  chords  that  vary  the  note  of  the  voice, 
and  it  is  the  muscles  moving  the   lips  that  vary  their  pressure 
on  the  reed,  and  of  course  vary  the  note  of  the  instrument. 

382.  The  skillful  singer  or  speaker  exhibits  much  skill  in 
managing  the  muscles  of  the  "  wind-chest."     He  keeps  it  all 
the  time  well  supplied  with  air,  so  that  but  a  comparatively 
slight  action  of  the  expiratory  muscles  will  suffice  to  throw  the 
air  against  the  vocal  ligaments  with  the  requisite  force.     But 
an  unskillful  singer  or  speaker  much  of  the  time  has  his  chest 
poorly  supplied  with  air,  and  so  speaks  or  sings,  as  it  is  expressed, 
from  the  top  of  the  chest.     It  costs  him,  therefore,  so  much  labor 
to  throw  out  the  air  with  sufficient  force,  that  he  is  soon  tired 
out.     The  necessity  of  keeping  the  chest  full  of  air,  in  order  to 
work  the  vocal  apparatus  easily,  may  be  illustrated  by  reference 
to  the  bagpipe.     If  the  bag  containing  the  air  be  well  filled,  a 
slight  pressure  of  the  arm  upon  it  will  force  the  air  through  the 
pipe  with  sufficient  rapidity  to  produce  the  sound.     But  if  the 


THE   VOICE.  259 


Tiring  out  the  vocal  muscles.     Vocul  apparatus  in  birds. 

bag  be  flaccid,  from  the  little  quantity  of  air  in  it,  a  very  strong 
pressure  of  the  arm  will  be  required  to  produce  the  same  effect. 

383.  But  it  is  not  the  muscles  of  the  chest  only  that  are  tired 
out  in  the  unskillful  singer  or  speaker,  but  also  the  muscles  of 
the  larynx  and  the  throat.     And  a  frequent  tiring  of  these 
muscles  weakens  the  force  of  the  parts,  and  often  at  length 
produces  disease.     Much  of  the  throat-disease  of  public  speakers 
comes  from  this  cause,  and  is  a  nervous  disease,  the  affection  of 
the  lining  membrane  of  the  throat  being  often  a  mere  accompa- 
niment.    This  result  is  more  apt  to  occur  when  the  nervous 
force  of  the  system  generally  is  impaired,  than  when  there  is  a 
state  of  vigor.     It  is  also  more  apt  to  occur  in  those  who  speak 
in  a  uniform  and  somewhat  monotonous  manner,  than  in  those 
who  have  much  variety  in  their  mode  of  speaking.     A  continua- 
tion of  precisely  the  same  muscular  effort  for  any  length  of  time  is 
apt  to  produce  painful  exhaustion,  while  a  much  greater  amount 
of  varied  muscular  effort  may  be  put  forth  without  weariness, 
or  even  with  pleasure. 

384.  It  would  be  interesting  to  trace  the  differences  in  the 
arrangement  of  the  vocal  apparatus  in  different  animals,  but  I 
will  only  notice  the  arrangement  which  we  find  in  birds.     The 
voice  of  birds  is  formed  not,  as  in  us,  at  the  top  of  the  wind- 
pipe, but  at  its  lowest  portion.     Like  the  human  voice,  it  is 
produced  by  the  vibration  of  sheets  of  membrane.     These  are 
placed  just  at  the  division  of  the  trachea,  where  its  two  branches 
go  off  to  supply  the  two  lungs  with  air.     The  voice  is  formed 
by  these  ligaments,  and  is  then  transmitted  through  the  column 
of  air  contained  in  the  whole  length  of  the    windpipe.     This 
column  of  air  must  have  some  influence  on  the  note  of  the  voice, 
according  to  its  length  and  diameter.     Birds,  therefore,  in  sing- 
ing different  notes  change  its  length  in  some  measure.     This  is 
easily  done,  as  the  windpipe  is  composed  of  rings  of  cartilages, 
connected  together  by  membranous  substance.     There  are  mus- 
cles indeed  up  and  down  the  tube,  for  the  purpose  of  shortening 
it  by  approximating  these  rings  to  each  other.     As  the  turkey 
gobbles  he  throws  his  head  up  and  down,  and  thus  shortens 
and  lengthens  the  trachea.     This  movement  is  quite  obvious 
also  in  the  canary  bird. 

385.  Having  thus  treated  of  the  formation  and  the  mod- 
ulation of  the  voice,  I  come  now  to  its  articulation,  which 
makes  it  the  grand  medium  of  intercourse  between  man  and 
man.     I  will  first  describe  the  parts  engaged  in  articulation,  and 
then  speak  of  the  agency  of  each  of  them. 


260  HUMAN  PHYSIOLOGY. 

Parts  engaged  in  the  articulation  of  the  voice. 

386.  The  vocal  tube,  which  I  have  described  as  extending 
from  the  larynx  to  the  outlets  of  the  mouth  and  the  nostrils, 
produces  all  the  variety  of  pronunciation  in  all  the  different  lan- 
guages of  our  globe.     It  is  all  one  cavity,  though  it  is  partially 
divided  by  partition  walls.     If  you  recur  to  Fig.  10,  on  page 
48,  you  will  see  a  representation  of  this  compound  cavity.     At 
the  top  of  the  trachea  d  you  see  the  epiglottis  c,  which  shuts 
down  upon  its  orifice  when  we  are  swallowing.     Above  this  is 
a  large  space  called  the  pharynx.     It  is  the  back  part  of  the 
throat,  which  we  can  see  behind  the  arch  of  the  palate  on 
looking  at  it  through  the  open  mouth.     Its  communication  with 
the  mouth  and  the  cavities  of  the  nose  is  regulated  by  the  palate 
g,  which  is  moved  by  muscles  into  the  different  positions  required. 
The  cavities  are  very  complicated,  having  several  partitions  par- 
tially dividing  them,  as  seen  in  Fig.  89,  and  they  communicate 
with  cells  in  the  bones  by  small  orifices.     That  very  movable 
organ,  the  tongue,  and  the  teeth  and  lips,  I  need  not  describe. 

387.  We  will  now  observe  the  agency  which  the  different 
parts  of  this  compound  vocal  tube  have  in  the  articulation  of  the 
voice.     Every  letter,  whether  it  be  a  vowel  or  a  consonant,  re- 
quires a  particular  position  of  the  different  parts  of  the  vocal  tube. 
In  some  letters  the  tongue  is  the  chief  agent  in  articulation,  in 
others  the  lips,  in  others  the  teeth,  in  others  the  palate,  and  there 
are  some  in  the  formation  of  which  the  cavities  of  the  nose  have 
an  important  agency.     I  will  notice  the  different  parts  separately. 

388.  The  tongue  has  been  considered  so  essential  to  speech, 
that  tongue  and  language  are  often  used  synonymously.     But 
though  it  does  perform  an  important  part  in  articulation,  it  is 
not  absolutely  essential.     Though  it  assists  in  the  formation  of 
many  of  the  alphabetical  elements,  it  is  the  principal  agent  in 
but  two  of  them,  I  and  r.     The  loss  then  of  this  busy  little 
organ  does  not  necessarily  produce  dumbness,  nor  even  impair 
to  any  great  extent,  in  some  cases  at  least,  the  power  of  speech. 
To  prove  this  I  will  cite  a  few  facts  which  appear  to  be  well 
authenticated.     The  Emperor  Justin  says  that  he  had  seen  ven- 
erable men  who,  after  their  tongues  had  been  cut  off  at  the  root, 
"complained  bitterly  of  the  torture  they  had  suffered."     He 
says  also  in  another  place  that  some  prisoners,  who  were  pun- 
ished in  this  barbarous  manner  by  Honorichius,  King  of  the 
Vandals,  "  perfectly  retained  their  speech."     But  there  are  cases 
more  thoroughly  attested,  having  been  examined  and  reported 
upon  by  scientific  observers.     A  boy,  who  lost  his  tongue  by 
disease  at  the  age  of  eight  years,  was  exhibited  publicly  because 


THE   VOICE.  261 


The  tongue  less  essential  than  commonly  supposed.     Dentals. 

he  could  talk  without  a  tongue.  At  the  request  of  the  members 
of  the  University  of  Saumur,  the  boy  was  brought  before  them 
by  his  friends.  After  a  strict  examination  they  were  perfectly 
satisfied  as  to  the  facts  in  the  case,  and  recorded  their  official 
testimony  to  that  effect.  A  very  interesting  account  is  given 
of  another  case  in  the  Philosophical  Transactions,  in  several 
papers  published  from  time  to  time  between  the  years  1742 
and  1747.  It  is  the  case  of  a  girl  who  lost  from  disease  the 
whole  of  her  tongue,  together  with  the  uvula,  (the  little  round 
body  which  hangs  down  from  the  middle  of  the  arch  of  the 
palate,)  and  yet  could  talk  and  swallow  as  well  as  any  one. 
So  perfect  was  her  articulation,  that  she  could  pronounce  with 
exactness  those  letters  which  commonly  require  the  agency  of 
the  tip  of  the  tongue.  She  could  sing  finely,  articulating  with 
the  same  clearness  as  when  she  talked.  The  sockets  of  the  teeth 
too  were  so  much  injured,  that  there  were  few  teeth,  and  these 
rose  so  little  above  the  gums,  that  they  could  not  render  much 
assistance,  if  any,  in  articulation.  This  case  was  investigated 
very  thoroughly.  The  account  was  giveii»to  the  Royal  Society, 
attested  by  the  minister  of  the  parish,  a  physician  of  repute, 
and  another  respectable  person.  The  Society,  not  wishing  to 
give  too  easy  a  credence  to  so  strange  a  case,  requested  another 
report  from  another  set  of  witnesses  appointed  by  themselves, 
arid  they  gave  them  a  series  of  questions  to  guide  them  in  their 
investigations.  The  report  which  they  made  out  coincided  very 
minutely  with  the  account  first  given.  The  case  excited  so 
much  interest  that  the  young  woman  was  at  length  brought  to 
London,  and  appeared  before  the  Royal  Society  to  satisfy  them 
that  she  could  really  talk  and  sing,  although  she  had  no  tongue. 

389.  Some  of  the  letters  are  formed  principally  by  the  teeth, 
as  c,  t,  s,  z.     They  are  therefore  called  Dentals.     It  is  the  too 
frequent  and  bungling  employment  of  some  of  these  which  con- 
stitutes lisping.     Those  who  have  a  tongue  too  large  for  the 
mouth  are  apt  to  lisp.     In   advanced  age,  when  the  teeth  are 
lost,  we   find   this  defect  of  lisping.     The  reason  is  obvious. 
When  the  teeth  are  gone,  the  sockets  gradually  become  oblit- 
erated, and  that  part  of  the  jaw-bone  where  the  teeth  were,  of 
course  diminishes  in  size,  making  the  mouth  too  small  for  the 
tongue. 

390.  The  letters,  in  the  articulation  of  which  the  lips  take 
the  lead  are  6,  p,  m,f,  v,w,  &c,  and  are  called  labials.     Chil- 
dren, when  they  first  begin  to  talk,  use  labials  freely,  because 
they  can  see  in  others  the  motions  necessary  for  their  pronunci 


262  HUMAN   PHYSIOLOGY. 

Labinls.     Reverberation  in  some  letters  in  the  nasal  cavities. 

ation,  and  then  imitate  them.  Hence  the  endearing  terms  used 
by  the  child  to  the  parent  are,  I  believe,  in  all  languages,  or 
nearly  all,  composed  of  labials  and  vowels.  And  too,  it  is  from 
the  delight  which  the  child  takes  in  repeating  over  and  over 
these  terms,  that  we  have  the  word  papa  and  mama,  instead 
of  pa  and  ma.  The  same  thing  can  be  observed  in  other  lan- 
guages as  well  as  the  English.  If  we  teach  a  child  to  say 
father  instead  of  papa,  he  finds  little  difficulty  in  articulating 
the  first  syllable,  because  it  begins  with  a  labial,/;  but  in  the 
last  syllable  he  will  at  first  substitute  for  th  the  labial  v,  making 
it  faver.  Intoxicated  persons,  their  lips  being  weak  and  trem- 
bling, are  apt  to  make  an  awkward  use  of  the  labials,  as  well  as 
of  those  letters  in  which  the  tongue  has  much  agency.  Per- 
sons with  large  lips  also  are  apt  to  use  the  labials  unskillfully. 
Sometimes  one  labial  is  used  for  another,  as  /  for  v,  and  p  for 
b.  This  is  very  common  among  the  Welsh.  Shakspeare  gives 
us  an  amusing  case  of  this  sort  in  Sir  Hugh  Evans  in  the  Merry 
Wives  of  Windsor.  "Ferry  goot,"  says  he,  "I  will  make  a 
prief  of  it  in  my  note  book."  And  so  he  says  prains  for  brains, 
peings  for  beings,  petter  for  better,  &c.  The  labial  w  is  some- 
times used  for  v,  thus,  winegar,  indiwisible,  werry  wigorous. 

391.  The  nasal  cavities,  it  is  obvious,  must  have   a  great 
influence  in  articulation.     The  letters  m  and  n  are  partly  nasal. 
In  pronouncing  m  at  the  end  of  a  syllable,  as  am,  em,  or  om, 
we  close  the  lips,  and  the  sound  issuing  from  the  larynx  rever- 
brates  in  the  cavities  of  the  nose.     You  can  perceive  this  rever- 
beration  by  pressing  gently  upon  the  nostrils  with  the  fingers 
while  pronouncing  this  syllable.     The  same  can  be  said  of  n, 
except  that  in  pronouncing  it  we  press  the  tip  of  the  tongue 
against  the  roof  of  the  mouth  just  behind  the  front  teeth,  pre- 
venting the  passage  of  the  air  out  through  the  mouth  in  this 
way,  instead  of  doing  it  by  closing  the  lips,  as  in  articulating 
m.     When  m  and  n  begin  syllables,  as  in  mo  and  no,  the  mouth 
is  opened  after  the  m  or  n  is  pronounced,  in  order  to  give  utter- 
ance to  the  next  letter.     These  are  two  distinct  acts,  but  the 
one  succeeds  the  other  so  quickly,  that  they  appear  to  be  a 
single  act.     The  nasal  sound  ng  is  the  one  which  we  employ  in 
humming.    Hence,  the  mouth  is  kept  closed  and  the  sound  issues 
from  the  orifices  of  the  nostrils. 

392.  A  reverberation  of  sound  in  the  back  part  of  the  mouth 
and  the  cavities  of  the  nose  constitutes  a  distinguishing  peculi- 
arity of  many  of  the  consonants.     Thus,  in  pronouncing  b  arid 
p.  the  lips   are  placed  precisely  in   the  same  manner,  and  the 


THE  VOICE.  263 


This  reverberation  in  some  consonants  and  not  in  others. 

only  difference  between  them  is  that  6  has  the  reverberation 
spoken  of,  but  p  has  not.  If  you  pronounce  these  two  letters 
in  the  syllables  op  and  ab,  for  example,  while  you  press  on  the 
nostrils  with  your  fingers,  you  can  feel  the  vibration  occasioned 
by  this  reverberation  in  pronouncing  6,  but  there  is  obviously 
none  in  pronouncing/).  This  reverberation  is  heard  in  the  follow- 
ing alphabetical  elements,  B,  D,  G,  V,  Z  (the  sound  of  s  in  the 
word  as),  Y,  W,  Th  (as  in  thou),  Zh  (the  sound  of  z  in  azure), 
Ng,  L,  M,  N,  R.  Those  which  have  not  this  reverberation  are 
P,  T,  K,  F,  S  (as  heard  in  sun),  H,  Wh  (as  heard  in  which), 
Th  (as  heard  in  thing),  Sh  (the  sound  of  s  in  sure).  That  you 
may  contrast  these  two  sets  of  alphabetical  elements  individually, 
I  place  them  here  in  two  rows.  B  is  like  P,  except  that  it  has 
a  reverberation,  and  so  on  through. 

B,  D,  G,  V,  Z,  Y,  W,    Th,  Zh,  Ng,  L,  M,  N,  R. 
P,  T,   K,  F,   S,  H,  Wh,  Th,  Sh. 

393.  In  what  is  commonly  called  speaking  through  the  nose 
the  reverberation  mentioned  above  is  disagreeably  strong.     The 
popular  idea  of  it  is  incorrect,  for  this  fault  occurs  in  those  who 
have  some  obstruction  to  the  free  passage  of  the  air  through 
the  nose.     This  obstruction  acts  like  the  pressing  of  the  nostrils 
with  the  fingers,  confining  more  or  less  the  body  of  air  con- 
tained in  the  nasal  passages.     It  is  the  vibration  of  this  air  thus 
partially  confined  in  tortuous  passages  that  produces  the  nasal 
twang.    Any  thing  therefore  which  prevents  the  free  outlet  of  the 
air  from  the  nose  will  occasion  it.     Pressing  the  fingers  on  the 
nostrils  while  speaking,  as  already  hinted,  will  produce  it.     A 
common  example  of  it  we  have  in  what  is  called  a  cold  in  the 
head.     The  snuff-taker  has  this  twang,  because  by  such  constant 
stimulation   of   the    lining   membrane   it   becomes   thickened. 
Those  who  have  this  fault  of  "  speaking  through  the  nose,"  do 
not  like  others  breathe  ordinarily  through  the  nose  alone,  but 
you  see  them  sitting  with  their  mouth  constantly  open,  showing 
that  there  is  so  much  obstruction  in  the  nasal  passages  that 
they  are  not  able  to  transmit  sufficient  air  to  the  lungs. 

394.  I  have  thus  far  spoken  of  articulation  as  employed  m 
ordinary  speech,  that  is  with  a  vocal  sound.     But  when  no 
sound  is  produced  by  the  ligaments  of  the  larynx,  as  is  the  case 
in  whispering,  the  noise  produced  by  the  passage  of  the  air 
through  the  cavities  of  the  vocal  apparatus  can  be  so  articulated, 
as  to  be  heard  distinctly  at  a  considerable  distance.     Persons, 
therefore,  who  have  entirely  lost  the  voice  can  converse.     In 


264 


HUMAN  PHYSIOLOGY. 


Variation  of  note  in  whispering.     Contrivances  to  imitate  articulation. 

whispering  the  vocal  ligaments  are  relaxed  as  they  are  when  we 
simply  breathe.  But  the  sound  of  whispering  has  its  high  and 
low  notes  like  the  vocal  sound.  The  variation  of  note  is  caused 
by  variation  of  the  size  of  the  column  of  air  contained  in  the 
vocal  tube.  This  is  effected  chiefly  by  the  tongue.  In  the  high 
notes  of  whispering  the  tongue  is  nearer  the  roof  of  the  mouth 
than  in  the  low  notes.  The  distinction  between  many  of  the 
letters  as  to  reverberation  noticed  in  §  392  holds  in  whispering 
as  it  does  in  ordinary  vocal  speech. 

395.  You  can  observe  the  mechanism  of  the  parts  that  is 
necessary  for  any  one  of  the  alphabetic  elements,  by  pronoun- 
cing some  syllable  which  it  ends,  prolonging  the  sound  of  the 
letter  in  question.     And  in  doing  this  you  will  readily  see  the 
incorrectness  of  the  common  definition  of  consonants,  viz.,  that 
they  are  letters  which  cannot  be  sounded  without  the  aid  of  a 
vowel.     Take,  for  instance,  the  lettter  m  in  the  syllable  am. 
After  getting  an  idea  of  the  mechanism  necessary  for  it  by 
sounding  it  with  a,  you  can  readily  sound  it  alone.     It  is  proper 
to  remark  here,  that  in  observing  the  distinctions  between  the 
alphabetical  elements,  you   must  bear  in  mind  that  the  names 
w^hich  are  given  to  the  letters  in  the  alphabet  do  not  represent 
their  sounds.     For  example, -H  (aitch)  and  W  (double-u)  are 
nothing  like  the  sound  of  these  letters  in  have  and  wave. 

396.  Various  attempts  have  been  made  to  imitate  the  artic- 
ulation of  sounds  by  mechanism,  but  with  very  limited  success. 
In  1779  a  prize  was  offered  by  the  Academy  of  Science  at  St. 
Petersburg,  for  the   best  dissertation  on  the  theory  of  vowel 
sounds,  and  it  was  awarded  to  G.  R.  Kratzanstein,  an  account 
of  whose  experiments  was  published  in  the  Transactions  of  the 
Academy.     He  found  that  the  sound  of  the  four  vowels,  A,  E, 
0  and  U,  might  be  produced  by  blowing  through  a  reed  into 
tubes,  the  forms  of  which  are  represented  in  Figures  142,  143, 
144  and  145,  and  that  the  sound  of  I,  as  pronounced  by  the 


FIG.  142      FIG.  143. 


FIG.  144. 


FIG.  145.        FIG.  146. 


THE   VOICE.  265 


Accurate  adjustment  of  vocal  and  articulating  muscles. 


French  and  other  European  nations  can  be  produced  by  blowing 
into  the  tube,  Fi<£.  146,  by  blowing  at  a  without  using  the  reed. 
M.  Kempelen,  of  Vienna,  the  inventor  of  Maelzel's  automaton 
chess-player,  carried  the  imitation  of  the  human  voice  still 
farther.  He  produced  an  instrument  capable  of  uttering  certain 
words  and  short  phrases  in  Latin  and  French.  But  it  is  not 
known  exactly  how  he  accomplished  this,  as  he  kept  the  matter 
secret.  A  gentleman  of  Cambridge,  England,  investigated  this 
subject,  and  among  other  things  found  that  by  blowing  through 
a  reed  into  a  conical  cavity,  the  vowel  sounds  could  be  pro- 
duced by  altering  the  size  of  the  aperture  for  the  passage  of  the 
air  from  the  cavity,  by  means  of  a  sliding  board.  I  have  alluded 
to  these  attempts  to  imitate  the  voice,  to  show  by  contrast 
the  wonderful  completeness  and  perfection  of  the  vocal  appa- 
ratus. Kempelen's  instrument,  a  box  three  feet  long,  could 
produce  only  a  few  words,  but  the  instrument  of  the  voice, 
although  it  occupies  so  little  room  in  the  body,  can  utter  all 
words  in  all  languages. 

397.  We  have  now  examined  the  whole  of  the  vocal  appa- 
ratus. You  will  observe  that  I  have  spoken  of  it  as  having  two 
parts,  the  larynx,  which  is  the  reed  of  the  instrument,  and  the 
vocal  tube,  which  you  have  seen  is  quite  complicated,  for  the 
purposes  of  articulation.  Every  action  in  both  parts  of  the  in- 
strument is  produced  by  muscles.  You  have  seen  that  the 
action  of  muscles  is  requisite  to  cause  any,  even  the  slightest, 
variation  of  note.  So  it  is  with  the  articulating  apparatus,  as 
it  may  be  called.  Every  alphabetical  element,  (and  in  our  lan- 
guage Rush  makes  35  in  the  whole,)  requires  a  particular  ad- 
justment of  the  articulating  apparatus.  This  adjustment  is 
effected  by  muscles  that  move  the  tongue,  lips,  palate,  &c.  As 
these  muscles  then  perform  such  varied  movements,  to  produce 
this  variety  of  note  and  articulation,  it  is  no  wonder  that  they 
require  such  long  and  diligent  training.-  The  child  begins  this 
long  course  of  education  the  moment  he  utters  an  articulate 
sound.  Observe  him  as  he  pronounces  the  syllable  pa  or  ma, 
the  first  which  children  generally  learn.  He  looks  at  his  mother's 
lips,  and  imitates  the  motion  as  well  as  he  can.  Cheered  by 
his  success,  and  by  her  approving  smile,  he  is  constantly  repeat- 
ing these  first  lessons  in  pronunciation  to  every  one  that  comes 
"near  him.  Being  as  yet  without  skill  in  the  use  of  these  organs, 
he  gives  much  more  force  than  is  necessary  to  the  mechanical 
motions  of  articulation.  For  example,  in  pronouncing  the  word 
pa,  he  closes  his  lips  strongly,  and  not  slightly  as  we  do,  and 

23 


266  HUMAN   PHYSIOLOGY. 

Training  of  the  muscles  in  speech.     Skill  in  their  use. 

when  he  opens  it  for  the  utterance  of  the  word  he  does  it  with  an 
explosive  force,  at  the  same  time  quickly  bowing  his  head.  The 
energy  of  his  whole  frame  seems  to  be  concentrated  upon  the 
effort.  Day  after  day  he  strives  to  add  to  his  stock  of  words, 
but  his  progress  is  slow  ;  and  as  a  sort  of  compensation  for  the 
leanness  of  his  stock  he  repeats  those  which  he  has  learned,  and 
so  of  his  own  accord  he  says  papa  and  mamma  instead  of  using 
the  words  of  a  single  syllable.  In  this  education  of  the  organs 
of  the  voice  the  ear  is  the  principal  instructor,  but  the  eye,  as 
you  see,  is  also  of  great  assistance.  The  little  pupil,  on  hearing 
a  sound  which  he  wishes  to  utter  himself,  tries  to  imitate  the 
motion  which  he  sees  is  used  in  producing  it,  and  he  continues 
to  try  till  his  ear  assures  him  that  he  has  actually  mastered 
the  sound.  Soon  he  is  able  to  utter  two  different  articulate 
sounds  in  succession ;  and  he  goes  on  learning  year  after  year, 
till  at  length  he  can  command  all  the  sounds  of  his  native 
tongue.  And  I  may  remark  that  it  is  in  childhood  and  youth 
alone,  that  we  can  learn  accurately  and  thoroughly  the  pronun- 
ciation of  a  language  that  is  at  all  difficult  in  this  respect. 
Hence  a  foreigner,  however  long  he  may  live  in  a  country,  to 
which  he  goes  in  adult  life,  cannot  wholly  conceal  his  native 
accent.  And  we  know  how  much  such  sounds  as  that  of  th 
trouble  the  German  and  the  Frenchman,  unless  they  begin  to 
learn  the  English  language  early  in  life. 

398.  If  we  observe  different  persons  while  speaking  or  sing- 
ing, we  shall  see  that  some  manage  the  vocal  apparatus,  or  play 
on  the  vocal  instrument,  as  we  may  express  it,  with  more  skill 
than  others.  Listen  to  two  persons  in  conversation,  the  one 
modulating  and  articulating  his  voice  with  a  graceful  melody, 
the  other  having  an  utterance  harsh  and  awkward ;  and  the 
contrast  is  as  great  as  that  between  two  instruments,  one  of 
which  is  well  and  the  other  badly  played.  In  some  you  can  al- 
most imagine  that  you  hear  the  creaking  of  the  machinery ;  while 
in  others  you  do  not  once  think  of  the  mechanism  of  the  voice, 
but  your  "ear  feasts  upon  its  richly  modulated  and  gracefully 
articulated  sounds.  It  is  as  true  of  the  muscles  of  the  vocal 
apparatus  as  of  those  of  any  other  part  of  the  body,  that  skill  in 
the  management  of  them  can  be  very  much  increased  by  exer- 
cise. The  rope-dancer,  by  training  his  muscles,  gives  them  a 
wonderful  precision  of  action.  The  same  thing  can  be  done 
with  the  muscles  that  regulate  the  modulation  and  articulation 
of  the  voice.  And  in  the  most  noted  singers  the  little  muscles 
which  move  the  vocal  ligaments  and  those  which  adjust  th> 


THE  VOICE.  267 


Stammering.    The  ear  the  instructor  of  the  voice. 


parts  of  the  vocal  tube,  must  have  a  precision  of  action  incom- 
parably more  accurate  and  delicate  than  the  large  muscles  in 
the  limbs  of  the  rope-dancer.  If  we  compare  the  limited  and 
bungling  operations  of  the  vocal  apparatus  in  a  little  child  just 
beginning  to  talk,  with  its  infinitely  varied  but  precise  move- 
ments in  a 'voluble  speaker,  or  a  skillful  singer,  we  shall  have 
some  conception  of  the  delicacy  of  motion,  of  which  the  muscles 
of  this  apparatus  become  capable  by  long  continued  exercise. 

399.  There  is  a  defective  action  of  the  muscles  of  the  vocal 
apparatus,  called  stammering  or  stuttering,  which  I -will  just 
notice.     It  is  an  irregular  spasmodic  action  of  these  muscles,  very 
much  like  that  which  we  see  in  the  muscles  of  other  parts  of 
the  body  in  the  disease  called  St.  Vitus'  dance.     It  is  very  much 
influenced  by  habit,  and  mental  agitation  aggravates  it.     Shak- 
speare  gives  the  following  accurate  description  of  it.     "I  would 
thou  wouldst  stammer,  that  thou  mightest  pour  out  of  thy  mouth, 
as  wine  comes  out  of  a  narrow  mouthed  bottle,  either  too  much 
at  once,  or  none  at  all."     It  is  a  singular  and  instructive  fact, 
that  many  who  stutter  in  ordinary  conversation  can  read  and 
sing  as  well  as  others.     Dr.  Good  remarks  that  one  of  the  worst 
stammerers  he  ever  knew  was  one  of  the  best  readers  of  Paradise 
Lost  that  he  ever  heard.     Such  facts  suggest  some   valuable 
principles  in  the  treatment  of  this  difficulty,  which  can  be  more 
easily  overcome  than  is  commonly  supposed. 

400.  Not  only  is  the  ear  the  educator  of  the  muscles  of  the 
voice,  but  the  dependence  upon  the  ear  is  entire.     The  deaf  and 
dumb  therefore  are  in  almost  every  case  dumb  because  they 
are  deaf.     Their  vocal  organs  are  in  a  good  condition,  and  the 
muscles  are  all  there  with  their  nervous  connections.     But  the 
machinery  does  not  work,  for  there  is  no  guiding  power  to 
direct  it.     That  this  is  the  true  view,  is  proved  by  those  cases  in 
which  hearing  has  been  restored,  for  such  restoration  is  followed 
by  that  of  the  power  of  speech.     Magendie  relates  an  interest- 
ing case  of  this  kind.     It  was  the  case  of  a  young  man  deaf 
and  dumb  from  birth,  who  had  his  hearing  restored  by  M.  Itard. 
He  first  heard  the  sound  of  the  neighboring  bells,  which  not 
only  caused  very  lively  emotions,  but  even  headache  and  dizzi- 
ness.    The  next  day  he  heard  the  sound  of  the  small  bell  in 
the  room,  and  shortly  after  he  could  hear  the  voice  of  persons 
speaking.     His  delight  was  then  extreme,  and  he  was  so  ab- 
sorbed in  his  new  enjoyment  that,  says  Professor  Percy,  "  his 
eyes  seemed  to  search  the  words  even  on  our  lips."     His  voice 
was  soon  developed.     The  muscles  of  the  vocal  organs,  so  long 


268  HUMAN   PHYSIOLOGY. 

Absolute  dependence  of  the  voice  upon  the  hearing.     Seen  in  the  denf  and  dumb. 

inactive,  began  to  wake  up  under  the  tuition  of  their  instructor, 
the  ear.  Only  vague  sounds  were  formed  at  first,  and,  although 
after  a  while  he  could  pronounce  some  words,  he  did  it  awk- 
wardly as  children  do  when  they  are  beginning  to  talk.  He 
learned  to  talk  very  slowly.  It  would  have  been  very  interest- 
ing to  have  watched  this  case  in  its  progress,  but  this  was  pre- 
vented by  a  disease  which  proved  fatal. 

401.  Few  cases  occur  like  that  which  is  related  above,  but 
there  are  many  cases  in  which  the  dependence  of  speech  upon 
hearing  is  proved  in  another  way.     I  refer  to  those  cases  in 
which  the  loss  of  the  power  of  speech  is  obviously  the  conse- 
quence of  the  loss  of  the  hearing.     This  is  the  case  with  children 
that  become  entirely  deaf  after  they  have  made  some  progress 
in  learning  to  talk.     They  cease  to  talk,  and  very  soon  forget 
the  motions  which  they  had  learned  to  make  in  articulation. 
Sometimes  some  of  these  motions  are  remembered,  and  the 
individual  can  pronounce  some  words.     But  he  does  it  very 
awkwardly,  and  the  consciousness  of  this  makes  him  very  averse 
to  trying  it.     A  friend  mentioned  to  me  the  case  of  a  man  who 
became  deaf  just  after  he  had  learned   the  alphabet.     He  re 
membered  the  mechanical  effort  necessary  to  produce  each  letter, 
but  he  had  no  control  over  the  loudness  or  note  of  the  voice,  so 
that  some  of  the  letters  he  sounded  very  high,  others  low,  some 
very  loud,  and  others  soft,  making  of  course  some  laughable 
contrasts.     It  is  undoubtedly  possible  to  teach  deaf  and  dumb 
persons  to  talk  to  some  extent,  if  we  begin  early  enough  ;  but 
the  power  of  speech,  after  the  most  persevering  training,  must 
be   awkwardly  mechanical,  and  exceedingly  limited.     Accord 
ingly  all  such  efforts  have  been  very  soon  given  up. 

402.  The  question  has  probably  arisen  in  your  minds  as  to 
what  the  difference  is  between  the  voice  of  speech  and  the  voice 
of  song.     The  common  notions  on  this  subject  were  very  indefi- 
nite until  recently.     But  Dr.  Rush,  in  his  admirable  work  on  the 
voice,  has  developed  the  true  principles  in  regard  to  it.     He 
has  shown  that  we  use  the  same  notes  in  speech  and  song,  and 
that  the  difference  lies  in  the  mode  of  using  them.     I  will  en- 
deavor to  place  before  you   the   most  prominent  and  material 
points  in  his  view  of  this  subject. 

403.  If  you  pronounce  the  sound  a  as  heard  in  day,  you  will 
observe  that  it  ends  in  another  sound,  that  of  e.     The  voice  in 
pronouncing  it  rises  through  the  interval  of  a  tone,  the  sound 
at  the  same  time  gradually  diminishing.     So  of  other  letters 
Thus,  a  as  sounded  in  awe,  ends  or  vanishes  in  e  as  heard  in  err;  o 


THE  VOICE.  26S 


Voice  of  speech  and  of  song.    Explanation  of  emphasis. 

as  heard  in  old  vanishes  in  oo  as  heard  in  ooze;  and  ou  as  heard 
in  our  vanishes  also  in  oo.  The  vanishing  sounds  are  of  course 
rather  obscure  and  feeble.  The  first  sound  he  calls  the  "  radical 
movement  of  the  voice,"  and  the  subsequent  diminishing  sound 
its  u  vanishing  movement."  The  rise  of  the  voice  during  the  van- 
ishing movement  is  not  always  through  the  interval  of  a  tone, 
but  it  may  be  only  a  semitone,  or  it  may  be  even  through  the 
interval  of  an  octave.  In  singing  the  movement  is  very  differ- 
ent. We  pass  "  quickly  and  faintly  through  the  radical  move- 
ment to  dwell  with  greater  time  and  fullness  on  a  note  or  level 
line  of  sound  at  the  extreme  place  of  the  vanish."  Both  in 
song  and  speech  there  is  also  a  downward  as  well  as  an  upward 
movement  on  the  scale.  The  gliding  of  the  voice  on  the  scale, 
and  its  gradual  vanish  cannot  be  imitated  on  instruments.  They 
may  be  imitated  to  some  extent  however  on  the  violin  if  the 
finger  moves  along  the  string  while  the  bow  is  drawn.  The 
difference  between  the  voice  of  speech  and  song  is  thus  repre- 
sented by  Dr.  Rush : 

VOICE  OF  SPEECH.  OF  SONG. 


At  1  is  represented  the  vanish  on  the  interval  of  a  tone ;  at  2 
on  that  of  a  third ;  at  3  on  that  of  a  fifth,  and  at  4  on  that  of 
an  octave. 

404.  I  will  notice  very  briefly  the  use  of  the  vanishing  move- 
ment in  speech.  In  simple  narrative  the  vanish  never  rises 
above  the  interval  of  a  tone,  as  at  1.  Whenever  it  rises  higher 
it  is  either  for  emphasis  or  interrogation.  The  vanish  on  the 
interval  of  a  fifth,  as  at  3,  is  the  most  common  mode  of  interro- 
gation. That  of  the  octave,  4,  is  used  when  the  question  is 
asked  with  great  vehemence,  or  is  accompanied  with  sneering, 
mirth,  contempt,  or  raillery.  Thus  when  the  Jew  in  the  Mer- 
chant of  Venice  asks, 

Hath  a  dog  money  ?     Is  it  possible 
A  cur  can  lend  ten  thousand  ducats  ? 

there  is  a  rise  through  the  interval  of  an  octave  on  the  words 
cur  and  dog.  You  observe  that  the  rise  is  on  the  words  which 
are  emphasized.  Thus  we  can  make  four  entirely  different 

23* 


270  HUMAN  PHYSIOLOGY. 

Use  of  the  semitone  in  speech.     Difference  in  capability  of  singing. 

sentences  of  the  question,  do  you  ride  to  town  to  day  ?  accord- 
ing as  we  make  the  rise  on  you,  or  ride,  or  town,  or  day.  By 
the  use  of  this  rising  vanish  we  can  make  a  question  of  the 
most  positive  assertion,  even  of  the  blunt  negative,  no. 

405.  The  vanish  on  the  interval  of  a  semitone  gives  the  voice 
a  plaintive  character,  and  it  is  therefore  used  for  the  expression 
of  love,  grief,  supplication,  &c.  It  is  sometimes  used  so  much 
as  to  give  a  general  character  of  plaintiveness  to  one's  whole 
conversation.  As  a  very  clear  and  striking  illustration  of  the 
power  of  the  semitone  we  will  take  the  cry  of  fire.  Divide  the 
word  into  two  syllables,  fi-yer,  and  ascend  the  scale  thus : 


Fi-yer.        Fi-yer         Fi-yer.  Fi-yer. 

The  two  places  of  the  semitones,  indicated  by  the  braces,  will 
give  the  cry  of  fire  as  we  commonly  hear  it.  Sometimes  we 
hear  it  cried  in  sport  upon  one  note,  and  the  sound  is  discordant 
and  ludicrous.  So  also,  the  two  words,  "0  dear,"  sound  like  a 
mere  mockery  of  grief,  if  uttered  on  one  note,  or  any  other 
interval  than  the  semitone. 

406.  Every  one  learns  to  talk,  but  there  are  many  who  do 
not  learn  to  sing.  Now  as  the  same  notes  are  used  in  the  two 
cases,  what  is  the  reason  of  the  difference?  The  reason  is  not 
in  an  absolute  inability  to  appreciate  the  variations  of  note  in 
sound,  for  these  are  practically  appreciated  in  the  use  of  the 
vanishing  rise  in  conversation.  There  are  two  reasons  for  the 
difference.  One  is  this.  As  the  transitions  of  the  voice  from 
one  part  of  the  scale  to  another  are  much  more  varied  in  song 
than  in  speech,  and  are  made  by  leaps  instead  of  slides,  song 
requires  greater  skill  than  speech  does  in  the  action  of  the  mus- 
cles. Another  reason  is,  that  speech  is  a  necessity,  and  song 
is  not.  We  learn  to  speak  therefore  as  a  matter  of  course,  but 
singing  is  a  mere  accomplishment.  If  it  were  learned  as  uni- 
versally as  speaking  is,  there  would  be  nearly  aL  much  good 
singing  as  good  speaking.  We  can  realize  the  truth  of  this 
assertion,  when  we  observe  the  results  of  very  early  training  in 
singing.  And  we  should  realize  it  still  more  if  singing  were 
universally  considered,  as  it  should  be,  as  an  essential  part  of 


THE   EAR.  271 


Ventriloquism.     Difference  between  a  sound  and  a  noise. 

the  education  of  children.  And  I  may  remark  in  this  connec- 
tion, that  all  have  some  measure  of  musical  talent,  though  in 
some  it  is  exceedingly  small  in  amount.  The  difference  in  this 
respect  in  different  persons  is  the  same  as  the  difference  in  re- 
gard to  any  other  talent,  as  that  of  drawing  for  example.  Skill 
is  acquired  in  the  same  way  in  both  cases,  and  its  degree  de- 
pends to  the  same  extent,  and  in  the  same  manner  upon  natural 
endowment. 

407.  Some  persons  possess  extraordinary  powers  in  the  use 
of  the  vocal  organs.  I  refer  to  ventriloquism.  This  is  a  purely 
imitative  art,  and  is  not  to  be  attributed  to  any  peculiar  forma- 
tion of  the  parts  in  the  individual  who  possesses  the  power. 
The  ventriloquist  must  have  the  faculty  of  appreciating  with 
great  accuracy  the  almost  infinite  variety  of  tones,  articulations, 
and  inflections  of  the  voice,  and  must  be  able  to  imitate  them 
with  but  little  motion  of  those  parts  of  the  articulating  apparatus 
which  appear  in  view.  He  at  the  same  time  makes  skillful  use 
of  those  circumstances,  which  will  favor  the  false  impressions 
in  the  minds  of  his  audience,  in  relation  to  the  locality  of  the 
source  of  the  sounds.  This  is  the  simple  explanation  of  this 
wonderful  power. 


CHAPTER  XV. 

THE  EAR. 

IN  the  last  chapter  I  treated  of  the  production  of  sound  by 
the  vocal  apparatus.  In  this  chapter  I  propose  to  show  you 
how  the  impression  of  sound  is  transmitted  to  the  brain,  in 
order  to  produce  the  sensation  of  hearing. 

408.  That  you  may  the  better  understand  the  arrangement 
of  the  apparatus  of  hearing,  I  will  first  notice  some  of  the 
principles  that  govern  the  transmission  of  sonorous  vibrations. 
Sound  may  be  produced  by  the  vibration  of  any  substance; 
though  some  are  better  fitted  to  produce  it  than  others,  and  are 
therefore  called  sonorous  bodies.  When  the  vibrations  which 
cause  sound  are  equal,  a  musical  sound  results ;  but  if  they  are 


272  HUMAN   PHYSIOLOGY. 


Reflection  of  sound.     Speaking  tube.     Ear  trumpet. 


unequal,  we  have  a  discordant  sound,  or  what  we  ordinarily 
call  a  noise.  Sound  is  transmitted  from  the  point  where  it 
originates,  in  all  directions.  And  its  vibrations  gradually  les- 
sen, just  as  the  ripples  lessen  which  are  produced  by  dropping 
a  stone  into  the  water.  The  vibrations  of  sound  are  reflected 
by  objects  against  which  they  strike.  For  this  reason  the  voice 
can  be  heard  at  a  much  greater  distance  if  it  be  transmitted 
along  a  wall  than  when  it  is  uttered  in  an  open  space.  This 
may  be  illustrated  on  Fig.  147.  Let  A  B  represent  a  wall,  and 

FIG.  147. 


C  the  position  of  the  ear.  If  the  bell  at  D  be  rung,  besides 
the  vibrations  which  come  to  the  ear  at  C  in  the  direct  line 
C  D,  a  vibration  striking  the  wall  at  F  will  come  to  the  ear  in 
the  line  F  C,  and  the  same  can  be  said  of  other  points  along 
the  wall.  An  accumulation  of  vibrations,  therefore,  comes  to 
the  ear  at  C,  which  therefore  receives  a  louder  sound  from  the 
bell  than  it  would  if  the  bell  were  rung  in  a  perfectly  open 
space.  For  the  same  reason  a  speaker  can  be  heard  much  more 
easily  within  walls  than  he  can  be  in  the  open  air.  The  sound 
is  reflected,  and,  therefore,  in  some  measure  concentrated  by  the 
walls.  In  speaking  tubes  this  reflection  and  concentration  are 
carried  to  a  still  greater  extent.  Sound  can  in  this  way  be 
heard  at  a  great  distance  from  its  source.  M.  Biot  found  that 
when  he  spoke  in  a  whisper  at  one  end  of  a  tube,  over  three 
thousand  feet  in  length,  he  was  distinctly  heard  at  the  other 
end;  so  entirely  do  the  walls  of  the  tube  prevent  the  diffusion 
of  the  vibration  in  the  air  around.  Speaking  tubes  are  there- 
fore used  to  a  great  extent  in  large  manufactories,  where  direc- 
tions need  to  be  given  continually  to  workmen  in  different  parts 
of  the  establishment.  The  flexible  tube,  now  so  commonly 
made  use  of  by  deaf  persons,  furnishes  another  illustration. 
The  vibrations  of  the  voice  received  by  the  trumpet  -shaped  end 
are  transmitted  through  the  tube  to  the  ear. 


THE   EAK.  273 


Difference  in  the  transmission  of  sound  through  solid,  liquids,  and  guses. 

409.  Sound  may  be  transmitted   through   any  substance^ 
whether  it  be  solid,  liquid,  or  gaseous.     It  cannot  be  trans- 
mitted through  a  vacuum,  for  there  is  nothing  there  to  vibrate. 
Sound  differs  in  this  respect  from  light,  which  passes  as  readily 
through  a  vacuum  as  it  does  through  any  transparent  substance. 
The  fact  that  sound  cannot  be  transmitted  through  a  vacuum 
is  often  illustrated  by  an  experiment  with  the  air-pump.     If  a 
bell  be  put  under  the  receiver,  and  be  set  to  ringing,  ?.«  the  air 
is  exhausted  by  the  pump,  the  sound  becomes  more  and  more 
faint,  and  at  length  it  is  not  heard  at  all.     For  the  same  reason, 
a  pistol  fired  on  the  summit  of  a  mountain,  gives  nothing  like 
so  loud  a  report  as  when  it  is  fired  in  the  valley  below.     The 
more  solid  the  medium  is  for  the  transmission  of  sound,  the 
more  readily  is  it  transmitted.     The  scratching  of  a  pin  at  the 
end  of  a  long  log  may  be  heard  by  the  ear  applied  to  the  other 
end,  although  it  cannot  be  heard  through  the  air,  at  even  the 
distance  of  a  few  feet.     Savages  are  in   the  habit  of  putting 
the  ear  to  the  ground  to  hear  the  step  of  their  enemies  when 
they  apprehend  their  approach.     A  deaf  gentleman,  resting 
the  bowl  of  his  pipe  on  his  daughter's  piano-forte  as  he  smoked, 
found  that  he  could  hear  the  music  with  great  distinctness;  and 
many  deaf  persons  can  hear  conversation,  by  holding  a  stick 
between  their  teeth,  while  the  other  end  rests  against  the  teeth 
of  the  person  speaking.     A  knowledge  of  the  ready  transmis- 
sion of  sound  through  solids  suggested  the  examination  of  the 
chest  in  disease  by  the  ear.     If  the  ear  be  applied  to  the  chest, 
the  various  sounds  produced  by  the  air,  as  it  passes  through 
the  bronchial  tubes  into  the  air  cells,  can  be  heard  through  the 
solid  walls  of  the  chest,  and  thus  the  state  of  the  lungs  can  be 
discovered.     Water  is  a  much  better  conductor  of  sonorous 
vibration  than  air,  though  it  is  not  as  good  an  one  as  a  solid 
substance.     The  force  of  the  vibration  is  lessened  more  gradu- 
ally in  water  than  in   air,  and  its  rate  of  progress  in  water  is, 
according  to  Chladni,  4,900  feet  in  a  second,  or  between  four 
and  five  times  as  great  as  in  air. 

410.  Sonorous  vibration   does  not  pass  readily  from  one 
medium  to  another.     Thus,  although  the  scratch  on  the  log  is 
heard  so  easily  by  the  ear  at  the  other  end,  if  the  ear  be 
removed  a  little  from   the  log,  it  does  not  hear  the  sound, 
because  the  vibration  is  so  much  lessened  in  passing  from  the 
solid  wood  to  the  air.     It  is  clear  that  the  more  unlike  the  two 
substances  are,  when  sound  passes  from  one  to  the  other,  the 
more  will  the  vibration  be  lessened ;  for  the  more  unlike  they 


274  HUMAN  PHYSIOLOGY. 

Hearing  a  compound  process.     Only  in  part  mechanical. 

are,  the  less  easily  will  the  one  take  the  vibration  from  tho 
other.  For  this  reason,  a  sonorous  vibration,  produced  in  a 
solid  body,  may  be  transmitted  to  water  with  much  less  loss  of 
intensity  or  force,  than  occurs  when  it  is  transmitted  to  air. 
Arid  it  may  be  remarked  in  this  connection,  that  when  vibra- 
tions are  transmitted  to  a  fluid,  from  air  or  from  a  solid,  the 
intervention  of  a  membrane  is  of  essential  service,  for  it  pre- 
sents a  firm  surface  upon  which  the  vibrations  can  be  received. 

411.  The  principles  which  I  have  thus  noticed  will  be  seen 
to  apply  to  the  arrangement  of  the  apparatus  of  hearing,  as 
we  proceed  in  the  examination  of  it.     It  has  various  parts  for 
the  different  portions  of  the  process  which  we  call  hearing.     I 
will  premise  a  mere  general  description  of  this  process,  before 
entering  upon  the  examination  of  the  apparatus  in  detail.     The 
vibrations  of  sound,  passing  into  the  ear  by  a  tube,  strike  at 
the  bottom  of  that  tube  upon  a  drum.     The  air  can  go  no  far- 
ther, for  this  drum  is  perfectly  air-tight.     It  communicates  its 
vibrations,  however,  to  the  drum,  which  transmits  them  to  a 
chain  of  four  little  bones,  the  last  of  which  transmits  them  to 
another  drum,  covering  an  opening  into  various  winding  pas- 
sages in  solid  bone.     In  these  passages  is  contained  a  limpid 
fluid,  which  is  put  in  motion  by  the  vibrations  of  the  drum  last 
mentioned.     So  much  for  the  mere  mechanical  part  of  the  pro- 
cess.    In  the  winding  passages  are  spread  out  the  minute  fibres 
of  the  nerve  of  hearing.     The  vibrations  of  the  liquid  in  these 
halls  of  audience,  as  we  may  call  them,  make  an  impression 
upon  these  nerves,  which  is  communicated  to  the  brain  through 
the  trunk  of  the  nerve,  and  this  completes  the  whole  process 
necessary  to  the  production  of  the  sensation  of  hearing. 

412.  The  parts  of  the  apparatus  of  hearing  may  be  seen  in 
Fig.  148.     The  internal  portions  are  made  rather  larger  than 
natural,  in  order  that  the  arrangement  may  be  more  clear.     At 
a  b  c  is  the  external  ear;  at  d  is  the  entrance  to  the  tube  of 
the  ear  f;  g  is  the  drum  of  the  ear  at  the  end  of  this  tube, 
called  the  membrane  of  the  tympanum ;  h  is  the  cavity  of  the 
tympanum,  the  chain  of  bones  which  it  contains  being  left  out, 
so  that  the  plan  of  the  apparatus  may  be  more  clear  to  you; 
k  is  the  Eustachian  tube,  which  makes  a  communication  be- 
tween the  back  of  the  throat  and  the  cavity  of  the  tympanum; 
n  is  a  part  of  the  winding  passages,  shaped  like  a  snail's  shell, 
and  is  therefore  called  the  cochlea;  at  m  are  three  other  wind- 
ing passages,  called,  from  their  form,  semi-circular  canals;  and 
at  /  is  the  vestibule,  or  common   hall  of  entrance  to  all  these 


THE  EAB. 


275 


The  parts  of  the  apparatus  of  hearing  described. 


FIG.  148. 


..-•a 


VERTICAL  SECTION  OF  THE  ORGAN  OF  HEARING. 

winding  passages.  In  the  cavity  of  the  tympanum,  on  the  side 
opposite  to  the  drum  of  the  ear,  you  see  two  holes.  These 
open  into  the  winding  passages,  the  larger  one  into  their  vesti- 
bule or  entrance  hall.  Both  of  these  holes  are  covered  by  a 
membrane,  and  to  the  membrane  of  the  larger  one  is  attached 
the  last  of  the  chain  of  bones.  At  o  is  the  trunk  of  the  nerve 
of  hearing,  and  at  e  e  is  the  bone  that  incloses  these  parts, 
which  is  so  hard  that  it  is  called  the  petrous,  or  rock-like  bone. 

Having  given  you  this  general  view  of  the  apparatus,  I  shall 
now  speak  of  each  part  more  particularly. 

413.  The  object  of  the  external  ear  is  to  collect  the  waves  of 
sound,  and  direct  them  into  the  tube  of  the  ear.  There  have 
been  many  speculations  in  regard  to  the  use  of  the  prominences 
and  ridges  of  the  external  ear,  but  they  are  fanciful  and  ground- 
less; and  its  surface  is  thus  diversified,  probably  for  the  sake 
of  making  this  organ  a  comely  one.  If  the  object  were  to  give 
it  the  best  shape  and  arrangement  for  collecting  the  vibrations 
of  sound,  it  would  have  had  a  different  shape  altogether,  and 


276  HUMAN   PHYSIOLOGY. 

External  ear.     Tube.     Ear-wax.     Drum  and  bones. 

would  have  been  arranged  with  muscles  which  could  turn  it  in 
different  directions,  as  is  the  case  with  many  animals.  The 
shape  of  the  external  ear  is  much  better  in  many  animals  than 
it  is  in  man,  if  we  consider  its  object  to  be  merely  the  collec- 
tion of  the  waves  of  sound.  The  endowment  is  in  this  case,  as 
well  as  in  every  other,  according  to  the  necessities  of  the  case. 
The  bat  is  guided  so  much  in  its  movements  by  the  sense  of 
hearing,  that  it  has  of  necessity  very  large  ears,  and  they  are 
so  shaped  as  to  collect,  in  the  best  possible  manner,  the  vibra- 
tions of  the  air.  With  proportionably  large,  and  similarly  shaped 
ears,  man  could  hear  much  better  than  he  now  does,  but  he  has 
no  need  of  such  ugly  appendages.  In  regard  to  the  motions 
of  the  ears  in  animals,  it  is  worthy  of  remark,  that  animals  of 
prey  can  turn  their  ears  forward  with  the  most  facility,  while 
timorous  animals  turn  their  ears  backward  to  keep  warned  of 
danger. 

414.  The  tube  of  the  ear  is  about  an  inch  long  in  the  adult. 
It  is  formed  of  cartilage  like  the  external  ear,  and  ends  at  the 
drum.     At  its  entrance  are  hairs  which  afford  some  protection 
against  intruders.     But  the  chief  protection  is  the  bitter  wax, 
which  is  secreted  by  little  glands,  situated  in  the  skin  of  the 
tube.     The  odor  from  this  secretion  so  effectually  keeps  out  the 
insects  from  this  open  entrance,  that  it  is  quite  a  rare  occurrence 
to  have  an  insect  get  into  the  ear.     And  when  one  does  get  in, 
the  wax  envelopes  him,  and  commonly  soon  destroys  him. 

415.  The  drum  of  the  ear,  which  makes  the  closed  end  of 
the  tube  above  described,  as  seen  at  g,  Fig.  148,  is  very  thin 
and  transparent.     On  the  other  side  of  it  is  the  cavity  of  the 
tympanum  h.     In  this  cavity  are  the  four  bones.     These  are 
represented  in  Fig.  149,  enlarged 

so  that  you  can  see  their  shape  F1G- 

distinctly.  They  are  named  from 
their  shapes.  They  are  the  mal- 
leus or  hammer  m;  the  incus 
or  anvil  ij  the  os  orbiculare,  or 
round  bone  o,  the  smallest  bone 
in  the  body ;  and  the  stapes  or 
stirrup-bone.  The  long  handle 
of  the  hammer  k  is  fastened  to 
the  middle  of  the  drum  of  the  ear.  The  little  round  bone  is 
fixed  between  the  slender  end  of  the  anvil,  and  the  top  of  the 
stirrup-bone.  In  Fig.  150  you  have  a  representation  of  these 
bones,  together  with  the  drum  of  the  ear.  While  the  end  of 


THE   EAR.  277 


Eustachinn  tube.     Winding  passages  of  the  internal  ear. 


the  handle  of  the  hammer  is  fastened  to  FIG-  150> 

the  middle  of  the  dram,  the  base  of  the 
stirrup  is  fastened  to  another  drum,  cover- 
ing the  hole  or  window,  opening  into  the 
vestibule  of  the  winding  passages.  There 
are  three  very  delicate  muscles  which  move 
these  bones.  One  of  them  relaxes  the 
drum  of  the  ear,  and  another  makes  it 

,      ,  ,          ,  .  .  DrtUAl   Or     1  ralti   &An 

more  tense;  and  thus  the  drum  is  put  into  whh  ^^^ 

the  right  states  of  tension,  to  accommodate 
it  to  the  various  kinds  of  vibration  that  come  to  it.  This  is  a 
matter  of  some  importance,  for  it  is  plain  that  while  a  relaxed 
drum  can  vibrate  properly  to  grave  sounds  that  enter  the  ear, 
it  must  be  tense,  in  order  to  respond  properly  to  the  vibrations 
of  the  air  in  the  higher  notes. 

416.  The  cavity  of  the  tympanum  (h  Fig.  148)  in  which  the 
little  bones  are,  and  which  is  beyond  the  drum,  communicates 
with  the  mouth  by  the  Eustachian   tube  k.     If  you  shut  your 
mouth,  and  close  the  nostrils  with  the  fingers,  and  then  perform 
the  action  of  blowing,  you  will  feel  the  air  enter  the  Eustachian 
tubes,  and  fill  the  cavity  of  the  tympanum.     The  chief  object 
of  this  communication  is  to  have  air  on  the  inside  as  well  as 
the   outside  of  the  drum,  so  that  it  may  vibrate  freely.     The 
cavity  of  the   tympanum   might  indeed  have   been   a  closed 
cavity,  containing  air.     But  it  would  then  have  been  very  much 
like  a  common  drum,  with  the  hole  in  its  side  closed.     This 
would  very  much  impair  the  vibration. 

417.  We  now  come  to  another  part  of  the  apparatus  of 
hearing — the  winding  passages.     These  are  inclosed,  as  I  have 
already  stated,  in  the  most  solid  bone  in  the  body.     They  are 
called  together,  very  appropriately,  the   labyrinth,  sometimes 
the  internal  ear.     This  is  really  the  essential  part  of  the  appara- 
tus.    Here  are  the  true  halls  of  audience,  where  the  nerve  is 
posted,  which  receives   the   messages  from  without,  and  trans- 
mits them  to  the  brain.     The  drum  of  the  ear  and  the  chain  of 
little  bones  may  be  destroyed,  and  yet,  if  these  winding  pas- 
sages remain  entire,  with  the  membranes  over  the  two  windows 
that  open  into  them,  the  hearing  will  not  be  lost ;  though  it 
will  be  less  perfect  than  it  is  when  the  whole  of  the  apparatus 
is  there,  and  in  good  order.     Sir  Astley  Cooper  relates  the  case 
of  a  gentleman,  who  lost  the  drums  of  both  ears  by  disease. 
By  shutting  his  mouth,  he  could  blow  the  air  out  through  his 
ears,  with  such  force  as  to  make  a  whistling  noise,  and  to  move 

24 


278 


HUMAN   PHYSIOLOGY. 


FIG.  151. 


Description  of  the  winding  passages.     Their  importance. 

the  hair  that  hung  from  his  temples.  Yet  he  was  not  only  able 
to  hear  with  ease  all  common  conversation,  but  he  had  a  nice 
appreciation  of  musical  sounds.  Sir  Astley  says  that  "  he 
played  well  on  the  flute,  and  had  frequently  borne  a  part  in  a 
concert ;  and  he  sung  with  much  taste,  and  perfectly  in  tune." 
418.  The  labyrinth  is  represented  much  magnified  in  Fig. 
151.  The  middle  part  of  it,  v,  is  the  vestibule.  From  this  go 
out  the  semi-circular  canals, 
fc,  y,  z,  on  the  upper  side,  and 
on  the  lower  the  winding  pas- 
sages of  the  cochlea,  k.  At  o 
you  see  the  opening  called  the 
fenestra  ovalis,  or  oval  win- 
dow. This  is  covered  by  a 
membrane,  on  which  presses 
the  base  of  the  stirrup-bone. 
You  see  another  opening  r, 
which  is  called  the  f en.es tra 
rotunda,  or  round  window. 
This  is  covered  with  a  mem- 
brane. Both  of  these  open- 
ings you  see  in  Fig.  148,  in 
the  cavity  of  the  tympanum, 
Opposite  to  the  drum  of  the 
ear.  In  these  winding  pas- 
sages is  a  watery  fluid,  the  vibrations  of  which,  acting  upon 
the  branches  of  the  nerve  distributed  there,  cause  the  sensation 
of  hearing.  Of  course,  if  either  of  the  membranes  covering  the 
openings  into  these  passages  be  destroyed  or  broken,  the  fluid 
will  run  out  from  the  ear,  and  there  can  be  no  more  hearing, 
although  the  rest  of  the  apparatus  is  perfect.  The  drum  wili 
continue  to  vibrate  as  sounds  strike  upon  it,  the  little  chain  of 
bones  will  repeat  the  vibration,  but  it  will  stop  at  the  end  of 
the  chain,  the  stirrup-like  bone.  So  too,  although  the  mem- 
branes may  be  entire,  and  the  whole  apparatus  may  be  perfect 
a*  a  piece  of  mechanism,  so  that  the  succession  of  vibrations 
from  the  air  without  through  the  drum  and  the  chain  of  bones, 
to  the  fluid  of  the  labyrinth,  is  uninterrupted,  if  the  nerve  of 
hearing  be  paralyzed,  so  that  it  cannot  be  impressed  with  the 
vibration  of  the  fluid  that  bathes  its  branches,  there  can  be  no 
hearing.  Partial  deafness  is  undoubtedly  often  owing  to  a 
thickening  of  the  fluid  in  these  passages,  or  to  a  partial  failure 
of  the  nerve  distributed  in  them. 


THE   EAR.  279 


Principles  of  transmission  of  sound  observed  in  the  arrangement. 

419.  It  will  be  proper  to  say  a  word  here  in  relation  to  the 
choice  of  a  fluid,  instead  of  a  solid  or  an  aeriform  substance,  as 
the  medium  through  which  the  impression  of  the  vibration  of 
sound  is  communicated  to  the  nerve.     It  is  better  than  a  solid 
would  be,  so  far  as  we  can  see,  because  no  arrangement  of  a 
vibrating  solid  with  the  minute  fibres  of  the  branches  of  the 
nerve  could  be  effectual,  and  at  the  same  time  so  little  liable 
to  derangement,  as  the  arrangement  of  nervous  fibres  immersed 
in  a  liquid,  and  the  whole   inclosed  in  solid  walls  of  bone.     It 
is  better  than  air  would  be,  for  at  least  two  reasons.     1st.  The 
vibrations  of  sound,  as  stated  in  §  409,  are  communicated  with 
much  more  ease  and  rapidity  through  water  than  through  air. 
This  we  see  to  be  a  consideration  of  some  importance,  when  we 
look  at  the  complicated  and  winding  passages  that  contain  the 
fluid.     2d.  There  is  not  as  much  loss  in  the  force  of  the  vibra- 
tion in  the  transmission  from  the  solid  stirrup-bone  through  the 
membrane  to  the  fluid,  as  there  would  be  if  the  transmission 
were  to  air. 

420.  The  whole  arrangement  in  regard  to  material  we  can 
see  to  be  admirable,  if  examined  in  relation  to  the  known  prin- 
ciples of  the  transmission  of  sound.     We  can  see  the  object  of 
the  chain  of  bones.     If  these  were  left  out  of  the  arrangement 
we  could  hear,  but  not  so  well  as  we  do  now.     For  it  has  been 
ascertained  by  experiment,  that  the  transmission  is  much  more 
perfect  when  the  vibration  passes,  as  in  the  case  of  the  ear, 
through  a  tense  membrane,  then  through  a  chain  of  solid  sub- 
stances, and  from  them  through  a  second  membrane  to  the 
fluid,  than  it  is  when  the  chain  of  solid  bodies  is  omitted,  and 
air  is  made  to  take  their  place.     And  when  the  vibration  has 
arrived  at  the  fluid  in  the  labyrinth,  there  is  a  contrivance  there 
for  increasing  its  intensity.     There  are   two  little  chalky  con- 
cretions suspended  in   this  fluid  by  nervous  fibres.     These  are 
found  in  all  mammalia,  and  in  fishes  they  are   quite  large   and 
hard.     This  being  the  case,  it  was  inferred  that  these   bodies 
have  some  important  influence  upon  the  transmission ;  and  it 
has  been  found  by  experiment  that  hard   bodies   thus   situated 
in  a  fluid  increase  the  sonorous  vibrations  in  their  neighborhood. 

421.  You  will  remember  that  there  are  two  openings  into 
the  labyrinth,  from  the  cavity  of  the  tympanum.     Both  are 
covered  by  membranes,  one  of  which  is  pressed  upon  by  the 
stirrup- bone,  while  the  other  is  free.     It  was  formerly  supposed 
that  the  second  opening  was  absolutely  essential  to  the  vibra- 
tion of  the  fluid  in  the  labyrinth.     For,  as  fluids  are  incoin- 


280  HUMAN  PHYSIOLOGY. 

Mode  of  vibration  of  the  fluid  in  the  winding  passages. 

pressible,  it  was  inferred  that,  as  the  stirrup-bone  communi- 
cated its  vibration  to  the  membrane  of  the  fenestra  ovalis,  the 
fluid  in  the  labyrinth  would  not  vibrate,  unless  there  was  another 
opening  some  where,  the  membrane  of  which  would  yield  to 
pressure.  This,  however,  has  been  ascertained  to  be  not  strictly 
true.  It  has  been  proved  by  experiment  that  a  sonorous  vibra- 
tion can  be  transmitted  through  a  confined  fluid.  Indeed  there 
are  some  animals  in  which  there  is  only  one  opening  into  the 
labyrinth.  But,  although  this  second  opening  is  not  essential  to 
the  vibration  of  the  liquid,  it  undoubtedly  makes  that  vibration 
more  perfect.  Although  the  second  opening  is  so  near  the 
first,  as  seen  in  the  cavity  of  the  tympanum,  (Fig.  148)  yet  in 
relation  to  the  arrangement  of  the  winding  passages  of  the 
labyrinth,  as  you  will  soon  see,  it  is  really  quite  at  the  other 
end  of  it.  The  vibration  then  may  be  considered  as  communi- 
cated through  a  long  tube,  which  has  a  membrane  at  both 
ends.  And  it  is  obvious  that  a  vibration  communicated  to  the 
membrane  at  one  end,  will  more  readily  move  the  fluid  through- 
out all  the  tube,  from  the  yielding  of  the  membrane  at  the 
other  end.  This  will  be  more  obvious,  as  I  describe  more  par- 
ticularly the  arrangement  of  the  passages  in  the  labyrinth, 
which  I  will  now  do. 

422.  To  recur  to  Fig.  151,  the  vestibule  v,  into  which  the 
fenestra  ovalis  o  opens,  is,  as  before  stated,  a  sort  of  common 
entrance  hall  to  all  the  passages  of  the  labyrinth.  I  have 
spoken  of  the  semi-circular  canals  #,  y,  and  z,  that  lead  out 
from  this.  These  are  simple  canals.  But  the  passages  of  the 
cochlea,  k,  are  very  complicated,  and  it  is  this  fact  that  has 
given  the  name  of  labyrinth  to  the  whole  of  the  internal  ear. 
The  vestibule  opens  into  the  cochlea  at  its  base.  Now,  the 
cochlea  is  so  divided,  that  the  passage  into  which  the  vestibule 
opens,  runs  around  the  pillar  in  the  middle  of  it  to  its  top, 
making  just  two  turns  and  a  half.  It  there  opens  into  another 
passage,  which  makes  two  turns  and  a  halfback  to  the  base  of 
the  cochlea.  This  passage  does  not  end  in  the  vestibule  where 
the  other  began,  but  it  ends  in  the  round  hole  r,  which  opens 
into  the  cavity  of  the  tympanum.  This  disposition  of  the 
parts  of  the  cochlea  may  be  seen  in  Fig.  152,  which  represents 
it  as  opened  to  show  the  arrangement  of  the  walls  of  the  two 
winding  galleries.  The  pillar  in  the  middle,  around  which 
these  dividing  walls  are  fastened,  expands  in  the  top  into  what 
is  called  a  cupola,  where  the  two  spiral  galleries  communicate 
together.  With  this  description,  you  can  understand  in  what 


THE   EAR.  281 


Distribution  of  the  nerve  of  hearing  in  the  cochlea. 


FIG. 152, 


THE    COCHLEA  OPENED. 

directions  the  vibration  is  transmitted,  when  it  is  received  from 
the  stirrup-bone,  at  the  door  of  the  labyrinth,  by  the  membrane 
which  covers  it.  It  travels  one  way  up  the  fluid  in  the  three 
semi-circular  canals.  It  travels  another  way  through  one  spiral 
gallery  in  the  cochlea  to  the  cupola,  and  then  down  the  other 
spiral  gallery,  reaching  at  length  the  membrane  of  thefenestra 
rotunda,  or  round  window. 

423.  I  will  now  describe  to  you  the  arrangement  of  the 
branches  of  the  nerve  of  hearing  in  these  passages.  The  ar- 
rangement is  different  in  the  vestibule  and  the  semi-circular 
canals  from  what  it  is  in  the  cochlea.  In  all  the  cavities  of  the 
labyrinth,  there  is  a  thin,  delicate  lining  of  membrane,  which 
secretes  a  watery  fluid.  In  the  vestibule  and  semi-circular 
canals,  there  is  a  second  membrane.  This  is  separate  from  the 
first  membrane,  and  lies  loose  in  the  cavities.  It  makes  a  close 
sac,  and  as  it  extends  from  the  vestibule  into  the  semi-circular 
canals,  it  is  very  irregular  in  its  form.  This  sac  contains  a  fluid, 
and  the  fluid  secreted  from  the  membrane  which  lines  the  bone 
bathes  the  outside  of  the  sac.  Now,  it  is  on  the  delicate  mem- 
brane which  forms  this  sac,  that  the  fibres  of  the  nerve  are 
distributed,  so  that  they  may  receive  the  impression  of  the 
vibration  of  the  fluid.  In  Fig.  153,  is  a  representation  of  this 
sac,  with  the  distribution  of  the  nerve.  At  1,  2,  and  3,  you 
see  the  parts  of  this  sac  which  line  the  semi-circular  canals. 
At  4  is  a  junction  of  two  of  these  canals,  for  what  purpose  we 
know  not.  At  6,  9,  10,  and  11,  are  seen  the  terminations  of 
branches  of  the  nerve.  At  8  and  13  are  two  of  these  branches 

24* 


282 


HUMAN   PHYSIOLOGY. 


Distribution  of  the  nerve  in  the  semi-circular  canals. 


FIG.  153. 


and  at  14  is  the  branch  of  the  nerve  which  goes  to  be  distrib- 
uted in  the  cochlea.     In  Fig.  154  is  represented  one  of  the  parts 


FIG.  154. 


THE  EAR.  283 


Beautiful  arrangement  of  the  nervous  fibrils  in  the  cochlea. 

where  the  nerve  terminates,  as  at  10  in  Fig.  153,  much  more 
highly  magnified.  You  see  the  loop-like  termination  of  th,j 
nervous  fibrils.  You  can  readily  see  that  every  vibration  of 
the  fluid  would  make  an  impression  upon  these  nervous  fibrils 
thus  distributed  upon  this  delicate  membrane,  which  has  the 
fluid  upon  both  sides  of  it. 

424.  The  distribution  of  the  nerve  is  after  a  different  man- 
ner in  the  cochlea.  Here  there  is  no  loose  membrane,  with  the 
nerve  distributed  upon  it,  and  the  fluid  each  side  of  it,  as  in 
the  vestibule  and  the  semi-circular  canals.  But  the  nerve  is 
distributed  upon  the  division  wall  of  the  galleries  in  a  very 
beautiful  manner.  This  is  represented  in  Fig.  155,  in  which  2 

FIG.  155. 


is  the  nerve,  and  3,  3,  3,  show  its  distribution.  These  fibrils 
lie  in  little  channels  in  a  lamina,  or  leaf  of  solid  bone.  But  the 
bone  extends  only  to  4,  4,  and  the  remainder  of  the  division 
wall  is  made  of  membrane,  represented  at  5,  5,  5.  At  7  is  the 
opening  in  the  cupola,  by  which  the  two  spiral  galleries  com- 
municate. At  1  you  have  these  parts  of  the  natural  size.  We 
know  not  exactly  how  this  mechanism  works,  but  the  proba- 
bility is,  that  the  nerve  receives  impressions  from  the  vibrations 
of  the  fluid  in  two  ways — directly  from  the  fluid  itself,  and  also 
from  the  vibration  of  the  membrane  to  which  the  extremities 
of  the  nerve  are  attached,  this  membrane  being  shaken  of 
course  by  the  vibrating  fluid. 

425.  Having  thus  described  the  parts  of  the  organ  of  hear- 
ing, I  will  trace  for  you,  with  some  particularity,  the  steps  of 


284  HUMAN  PHYSIOLOGY. 

Steps  of  the  process  of  hearing  given  in  their  order. 

the  process  of  hearing,  as  it  must  occur  in  the  case  of  every 
sound  that  produces  that  sensation.  The  vibrating  air  enters 
the  tube  of  the  ear,  and,  reaching  the  drum,  produces  a  vibra- 
tion there.  This  vibration  is  communicated  to  the  chain  of 
bones,  which,  as  Dr.  Paley  very  aptly  says,  like  a  repeating 
line  of  frigates  pass  it  on.  It  is  transmitted  from  the  last  of 
this  chain  of  bones,  the  stirrup-bone,  to  the  membrane  covering 
thefenestra  ovalis,  and  from  this  to  the  fluid  contained  in  all 
the  passages  of  the  labyrinth.  The  vibration  goes  through  all 
the  semi-circular  cr.nals  in  one  direction,  and  in  another  up  one 
gallery  of  the  cochlea,  and  down  the  other.  In  all  these  cavi- 
ties, are  spread  out  in  various  ways,  the  filaments  of  the  nerve 
which  receive  the  impression  of  the  vibration.  This  impression 
is  transmitted  from  the  extremities  of  the  nerve,  through  its 
trunk,  to  the  brain,  where  the  mind  receives  it.  All  this  to- 
gether constitutes  hearing ;  and  all  of  it  occurs  in  the  case  of 
any  sound  which  we  hear,  however  closely  it  may  follow  any 
other  sound. 

426.  Most  of  our   hearing   is   done   precisely  in   the   way 
described,  but  not  all.     We  sometimes  hear  directly  through 
the  bone  surrounding  the  labyrinth.     If  you  place  a  watch 
between  the  teeth,  you  hear  the  ticking ;  and  it  gives  a  very 
different  sound  from  what  it  does  when  held  to  the  ear,  be- 
cause the  sonorous  vibration  is  transmitted  directly  through 
the  solid  bones  of  the  skull  from  the  teeth.     In  the  same  way 
was  the  sound  transmitted  in  the  case  of  the  deaf  old  gentle- 
man,  (§  409)  who    heard  his    daughter's  music  through  tho 
stem  of  his  pipe,  as  he  rested  the  bowl  of  it  on   the  piano. 
The  fact  thus  illustrated  is  often  made  use  of  by  physicians,  in 
detecting  the  nature  of  the  difficulty  in  cases  of  deafness.    Thus, 
if  a  watch  held  between  the  teeth  communicate  a  very  distinct 
and  loud  sound  to  the  ear,  we  infer  that  the  internal  ear  is  in  a 
good  condition,  and  that  the  difficulty  is  in  some  of  the  other 
parts  connected  with  it,  the  drum,  or  the  cavity  of  the  tym- 
panum, or  the  Eustachian  tube. 

427.  I  have  described  the  apparatus  of  hearing  as  we  find  it 
in  man.     But  it  varies  in  different  animals,  according  to  the 
circumstances  in  which  they  are  placed,  and  their  necessities. 
Animals  that  live  in  water  of  course  have  a  different  appa- 
ratus of  hearing  from  those  that  live  in  air.     In  most  fishes  the 
semi-circular  canals  exist,  but  there  is  nothing  like  a  cochlea. 
As  sounds  are  transmitted  so  easily  through  water,  (§  410,) 
fishes  have  no  need  of  so  complicated  and  perfect  an  apparatus 


THE   EAR.  285 


Hearing  in  other  animals.     Only  a  part  of  the  process  of  hearing  understood. 

as  animals  that  live  in  air.  They  are  fitted  to  hear  in  their  own 
element,  and  probably  the  moment  that  a  fish  is  taken  out  of 
the  water  he  becomes  quite  deaf,  because  his  hearing  apparatus 
is  so  poorly  fitted  to  receive  and  transmit  vibrations  from  the 
air.  But  in  many  animals  that  live  in  air  the  ear  differs  from 
that  of  man  in  its  arrangements.  The  cochlea  in  birds  is  nearly 
straight  instead  of  being  spiral.  Such  facts  lead  to  the  infer- 
ence, that  the  peculiar  arrangements  in  the  hearing  apparatus 
of  man  have  regard,  not  merely  to  the  medium  in  which  he  is 
placed,  but  to  peculiar  uses  which  are  necessary  in  his  case,  as 
the  determination  of  the  direction  of  sound,  the  appreciation 
of  its  pitch  and  its  character,  the  power  of  hearing  very  slight 
sounds,  &c.  The  simplest  form  of  apparatus  found  in  animals, 
is  a  cavity  excavated  in  bone,  with  a  fluid  shut  in  it  by  a  mem- 
brane, and  nervous  filaments  distributed  so  as  to  be  impressed 
by  the  vibrations  of  the  fluid.  And  this  is  all  that  is  absolutely 
essential  to  hearing. 

428.  Many  speculations  have  been  broached  in  regard  to  the 
special  offices  of  particular  parts  of  the  labyrinth.     Thus,  it  has 
been  supposed  that  the  semi-circular  canals  have  an  agency  in 
informing  us  of  the  direction  of  sounds ;  for  it  is  observed  that 
they  are  always  arranged  in   the  same  relative  angle  to  each 
other.     It  has  been  supposed  also,  that  the  cochlea  gives  us  the 
idea  of  the  note  of  sounds,  because  it  is  noticed  that  the  devel- 
opment of  this  part  in  different  animals  is  in  proportion  to  the 
variety  of  note  which  they  produce.     These  suppositions,  though 
quite  probable,  require  farther  investigation  in  comparative  anat- 
omy to  test  their  truth. 

429.  In  the  process  that  makes  up  the  sensation  of  hearing, 
there  is  one  part  which  we  can  in  some  measure  understand, 
and  to  which  we  can  apply  the  known  principles  which  govern 
the  transmission  of  sonorous  vibrations.     But  there  is  another 
part,  that  which  links  the  process  to  the  immaterial  mind,  that 
we  cannot  understand.     We  can  trace  the  vibration  received 
from  the  air  through  the  several  parts  to  the  fluid  in  the  laby- 
rinth, but  here  we  come  to  a  stand  in  our  knowledge.     The 
vibration  stops  here,  and  what  is  transmitted  through  the  nerve 
to  the  mind  we  know  not.     We  call  it  an  impression;  but  this 
is  only  an  indefinite  word,  implying  simply  that  something  is 
transmitted,  without  defining  what  it  is.     Neither  do  we  know 
how  the  transmission  is  made.     All  that  we  do  know  is,  that 
the  nerve  is  essential  to  the  completion  of  the  sensation  of  hear- 
ing, and  that  it  spreads  out  its  minute  fibrils  or  tubuli  in  the 


286  HUMAN  PHYSIOLOGY. 

Ear  equal  to  the  eye  in  delicacy,  beauty,  and  complication  of  structure. 

halls  of  audience,  in  order  to  receive  impressions  from  the  vi- 
brations that  come  there,  and  transmit  them  to  the  brain  where 
the  mind  takes  cognizance  of  them.  Every  part  of  the  appa- 
ratus may  be  mechanically  perfect,  so  that  the  vibrations 
may  be  transmitted  to  the  fluid  which  bathes  the  nervous 
fibrils,  but  if  the  nerve  be  paralyzed,  or  if  the  communication 
between  its  extreme  fibrils  and  the  brain  be  in  any  way  inter- 
rupted, the  mind  knows  nothing  of  the  vibration,  and  there  is 
no  hearing. 

430.  The  eye  has  generally  been  spoken  of  as  being  more 
wonderful  than  any  other  organ  in  the  body,  in  view  alike  of 
the  delicacy,  the  beauty,  and  the  complication  of  its  structure. 
But  the  apparatus^  of  hearing  presents  a  combination  of  these 
qualities  quite  as  wonderful.  There  is  nothing  more  delicate, 
and  beautiful,  and  complicated  than  the  arrangement  of  the 
nervous  fibrils  in  the  winding  labyrinthic  passages  of  the  halls 
of  audience.  And  as  we  trace  the  steps  of  the  process  of 
hearing,  from  the  drum  of  the  ear  where  the  sound  strikes,  to 
the  gray  substance  of  the  brain  where  the  mind  receives  the 
impression,  and  think  of  each  sound  as  sending  a  vibration 
through  membranes  and  a  chain  of  bones  to  the  fluid  in  which 
the  nervous  fibrils  are  immersed,  and  of  these  fibrils  as  catching 
from  every  vibration  of  the  fluid  a  definite  impression  and 
transmitting  it  to  the  mind,  we  see  a  mingling  of  the  purely 
mechanical  with  the  spiritual,  which  greatly  enhances  our  ad- 
miration of  the  mechanism.  Though  the  apparatus  is  compli- 
cated, the  mechanical  result  is  a  simple  one — it  is  a  mere 
trembling  of  a  fluid  inclosed  in  winding  cavities  of  bone.  But 
simple  as  the  result  is,  it  is  made,  through  the  beautiful  nervous 
connections  of  the  ear  with  the  brain,  one  of  the  chief  inlets  of 
knowledge  to  the  mind,  coming  to  it  from  nature's  multitudinous 
voices,  and  is  a  constant  medium  of  communication  for  thought 
and  feeling  between  man  and  man.  Thus  intimately  in  the 
human  body  are  the  simplest  mechanical  results  connected  with 
the  complicated  and  diversified  operations  of  the  mind.  In  the 
process  of  hearing  the  drum  of  the  ear  is  to  be  considered  one 
end  of  the  apparatus,  and  the  gray  portion  of  the  brain  the 
other.  The  drum  simply  vibrates ;  and  instantaneously  the 
mind  receives  a  distinct  impression  from  the  vesicles  of  the  gray 
matter.  And  thus  is  the  communication  established  between 
the  immaterial  mind,  and  the  vibrations  of  the  material  sub- 
stances with  which  it  is  surrounded. 


THE  EYE.  287 


Seeing  a  compound  process.     Refraction  of  light. 


CHAPTER    XVI. 

THE  EYE. 

431.  THE  sensation  of  sight  is  the  result  of  a  compound 
process,  which  may  be  divided  into  two  distinct  parts,  as  I  re- 
marked in  relation  to  the  sensation  of  hearing,  in  §  429.     The 
one  part  is  purely  mechanical,  and  the  apparatus  for  it  is  con- 
structed according  to  the  common  principles,  which  we  find 
illustrated  in  optical  instruments.     The  object  of  its  arrange- 
ments is  to  form  distinct  images  of  objects  in  the  back  part  of 
the  eye.     The  other  part  of  the  process  is  executed  by  the  nerve 
of  vision,  called  the  optic  nerve.     This  nerve,  expanded  upon 
the  membrane  where  the  images  are  formed,  transmits  impres- 
sions from  these  images  to  the  brain,  just  as  the  nerve  of  hearing 
transmits  to  the  brain  the  impressions  which  come  from  the 
vibration  of  the  fluid  of  the  labyrinth. 

Before  proceeding  to  an  examination  of  the  eye  as  an  optical 
instrument,  I  will  call  your  attention  to  certain  principles,  which 
we  shall  find  illustrated  more  beautifully  and  perfectly  in  the 
eye  than  in  any  optical  instrument  which  man  has  ever  con- 
structed. 

432.  The  rays  of  light  coming  from  any  luminous  point  go 
in  straight  lines  in  all  directions,  just  as  the  vibrations  of  sound 
do,  and,  like  them,  become  less  intense  the  farther  they  are 
diffused.     But  they  move  in  straight  lines  only  so  long  as  they 
remain  in  the  same  medium.     When  they  pass  from  one  me- 
dium into  another  they  are  bent  out  of  their  straight  course, 
or  refracted,  as  it  is  termed,  unless  they  pass  from  one  to  the 
other  in  lines  perpendicular  to  the 

surface  of  the  medium  which  they  FIG.  156. 

enter.  This  may  be  illustrated  by 
the  following  experiment.  Place 
a  coin,  a,  in  the  bottom  of  a  basin, 
as  represented  in  Fig.  156,  and  then 
withdraw  from  it  so  far  that  the 
coin  may  be  hidden  from  your  eye 
by  the  edge  of  the  basin,  as  repre- 
sented in  the  figure.  Keeping  your 
eye  fixed  in  that  position,  pour  some 


288  HUMAN  PHYSIOLOGY. 


Refraction  as  light  passes  from  a  rarer  into  a  denser  medium,  and  vice  versa. 

water  into  the  basin  up  to  the  level,  c.  The  coin  will  again 
become  visible  to  your  eye.  The  reason  is,  that  the  rays  of 
light,  as  they  come  from  the  water  into  the  rarer  medium,  the 
air,  are  refracted  or  bent  downwards,  that  is  from  the  perpen- 
dicular. The  effect  of  this  may  be  seen  in  the  figure.  A  ray 
of  light,  coming  from  the  coin  in  the  direction  a,  d,  does  not 
pass  to  d,  but  is  bent  downward,  and  so  passes  to  the  eye  at 
e.  And  so  of  other  rays  coming  from  the  object.  The  coin, 
therefore,  is  seen  by  the  eye  at  e,  but  it  is  not  seen  in  its  true 
direction  from  the  eye  which  is  in  the  line  e,  c,  a.  The  only  point 
in  which  the  eye  can  see  the  coin  in  its  true  position  is  when 
the  eye  is  at  £>,  in  a  perpendicular  line  directly  over  it.  A  ray 
that  passes  from  one  medium  to  another  in  a  line  perpendicular 
to  the  surface  of  the  medium  into  which  it  passes  is  not  bent 
out  of  its  course.  All  other  rays  are,  and  the  more  so  the 
farther  they  are  from  the  perpendicular. 

433.  While  rays  that  pass  from  a  dense  medium   into  a 
rarer,  as  from  water  into  air,  are  bent  from  the  perpendicular, 
those  on  the  other  hand,  which  pass  from  a  rarer  medium  into 
a  denser,  as  from  air  into  water,  are  bent  towards  the  perpendic- 
ular.    Thus  if  in  Fig.  156  a  be  the  position  of  the  eye  of  a 
fish,  and  where  the  eye  is,  at  e,  there  be  an  insect,  the  fish  can 
see  it,  because  the  ray  that  strikes  the  surface  of  the  water,  c, 
is  refracted  or  bent  towards  the  perpendicular  line,  6,  a.     And 
so  of  other  rays.     He  does  not  see  the  insect,  however,  in  its 
true  direction,  a,  c,  e,  but  it  appears  to  him  to  be  at  d.     For  we 
always  judge  of  the  place  of  an  object  by  the  direction  in 
which  the  rays  from  it  strike  the  eye. 

434.  When  light  passes  from  one  medium  into  another  which 
presents  a  convex  or  concave  surface,  instead  of  a  flat  one,  a 
very  great  change  is  produced  in  the  direction  of  its  rays. 
Thus  suppose,  as  represented  in  Fig.  157,  three  diverging  rays 
coming  from  a  point,  a,  through  the  air,  enter  a  convex  surface 
of  glass,  6,  6'.     The  central  ray  a,  c  enters  the  glass  in  a  direc- 
tion perpendicular  to  its  surface,  and  therefore  does  not  bend 
from  its  course.     But  the  ray  a,  d  enters  very  obliquely,  and  is 
bent  towards  the  perpendicular  at  that  point,  e,  and  passes  on 
in  the  direction  /.     So  likewise  the  ray,  a,  <7,  is  bent  towards 
the  perpendicular  A,  and  passes  on  in  the  line  i.     These  rays 
diverging  in  the  air  have  become  converging  in  the  glass,  and 
the  point  at  which  they  meet  is  called  the  focus.     To  this  point 
all  the  other  rays  entering  the  convex  glass  converge  also. 

435.  But  if  the  surface  of  the  glass  be  concave,  as  represented 


THE   EYE. 


289 


Refraction  by  convex  and  concave  lenses. 


in  Fig.  158.  the  diverging  rays  which  enter  it  will  be  made  to 
diverge  still  more.  The  ray,  a,  c,  being  perpendicular  to  the  sur- 
face is  unchanged  in  its  course ;  but  the  ray,  o,  c?,  is  bent  towards 
the  perpendicular,  e,  into  the  line/,  and  the  ray,  a)t/,  is  bent  to- 
wards the  perpendicular  h  into  the  line  t.  In  the  case  of  both 


FIG.  158. 


the  concave  and  the  convex  lens,  the  greater  the  curvature,  the 
greater  is  the  change  of  direction  in  the  rays.  The  greater  the 
curvature,  therefore,  the  sooner  are  the  rays  brought  to  a  focus 
in  the  case  of  the  convex  lens. 

There  are  other  optical  principles  illustrated  in  the  apparatus 
of  vision,  that  will  be  brought  out  in  the  description  of  the 
eye,  which  I  will  now  proceed  to  give. 

436.  The  arrangement  of  the  different  parts  of  the  eye  you 
can  understand  by  Fig.  159,  which  is  a  mere  map  of  a  section 
of  the  eye,  through  its  middle  part  from  front  to  rear.  It  is 
intended  merely  to  represent  the  arrangement  of  the  parts  dis- 
tinctly, without  strict  regard  to  proportion.  The  eye  has  three 

25 


290  HUMAN   PHYSIOLOGY. 


Description  of  the  parts  of  the  eye. 


FIG.  159. 


CL        I 

DIFFERENT  PARTS   OF  THE  EYE. 


coats,  as  they  are  called.  At  a  is  the  thick  strong  white  coat, 
called  the  sclerotic  coat,  from  a  Greek  word  meaning  hard, 
This,  which  is  commonly  called  the  white  of  the  eye,  gives  to 
the  eyeball  its  firmness.  Into  it  the  cornea,  e,  fits,  like  a  watch- 
glass  into  its  case.  The  sclerotic  and  cornea  then  make  one  coat 
of  the  eye,  the  o\iter  one.  Next  comes  the  choroid  coat,  b.  This 
is  a  very  vascular  coat,  containing  the  minute  branches  of  blood 
vessels  which  nourish  other  parts  of  the  eye.  It  is  of  a  dark 
color,  for  reasons  which  I  will  state  in  another  place.  Its  color 
is  owing  to  coloring  matter  contained  in  pigment  cells,  which 
lie.  along  on  the  inner  surface  of  this  coat,  next  to  the  inner 
coat  of  the  eye,  the  retina,  c.  The  retina  is  a  thin  membrane, 
being  principally  composed  of  the  expansion  of  the  optic  nerve, 
d.  The  eye  has  three  humors,  as  they  are  termed.  The  first 
is  the  aqueous  or  watery  humor,/",  which  is  in  a  chamber  be- 
tween the  transparent  cornea,  e,  and  the  crystalline  humor,  or 
lens,  h.  This  chamber  is  divided  into  two  parts  by  the  iris,  g, 
<7,  the  pupil  being  the  circular  communicating  door  between 
them.  The  part  of  the  chamber  which  is  in  front  o^f  the  iris 
is  much  larger  than  that  which  is  behind  it.  The  crystalline 
humor,  or  lens,  as  it  is  more  often  called,  has  the  consistency 
of  half  dissolved  glue.  At  i  is  the  vitreous  humor,  filling  up 
a  large  part  of  the  cavity  of  the  eye.  It  is  called  vitreous  from 
its  glassy  appearance.  It  is  a  clear,  jelly-like  substance,  having 
about  the  tenacity  of  white  of  egg.  It  is  contained  in  an  ex- 


THE   EYE. 


291 


Arrangement  of  the  front  part  of  the  eyeball. 


ceedingly  thin  and  delicate  sac,  and  this  is  divided  into  cells 
which  contain  the  liquid. 

437.  Fig.  160  is  a  map  of  the  front  part  of  the  eye,  in  which 
the  parts  are  more  minutely  delineated  than  in  Fig  159.     At  2 
is  the  sclerotic  coat ;  3,  the  cor- 
nea ;   6,  the  crystalline  lens  ;  a,  a, 

a,  the  aqueous  humor;  7,  7,  the 
iris ;  4,  the  choroid  coat ;  8,  the 
retina;  c,  c,  the  vitreous  humor, 
and  9,  the  sac  containing  it. 
Around  the  inside  of  the  cham- 
ber containing  the  aqueous  hu- 
mor is  a  very  thin  membrane, 
(represented  as  you  see  by  a  line,) 
which  secretes  the  humor.  In 
this  membrane,  as  in  the  case  of 
every  other  closed  sac  in  the  body, 
there  are  both  exhalents  and  ab- 
sorbents, so  that  the  fluid  may  be 
changed  as  necessity  requires. 
There  is  another  thin  membrane 
of  the  eye  which  I  have  not  yet 
described.  It  is  represented  by  a 
line,  1,  in  the  figure.  It  is  the 
conjunctiva,  so  called  because  it 
unites  or  conjoins  the  ball  of  the 
eye  with  the  eyelids.  It  covers 
the  cornea,  passes  back  a  little  way  on  the  white  of  the  eye, 
and  then  turns  forward  to  line  the  eyelid.  It  is  the  seat  of  the 
most  common  form  of  inflammation  in  the  eye.  It  is  very  vas- 
cular, as  is  shown  by  its  distended  vessels  when  it  is  inflamed. 
It  is  exceedingly  sensitive,  and  hence  the  great  pain  which  is 
occasioned  by  any  thing,  even  the  smallest  mote,  that  gets  into 
the  eye.  The  object  of  having  it  so  sensitive  I  have  spoken 
of  in  the  Chapter  on  the  Nervous  System,  §  242. 

438.  At  6  in  Fig.  160,  is  one  of  the  ciliary  processes,  as  they 
are  called,  from  their  resemblance  to  the  eyelashes.     There  is  a 
circular  row  of  them,  numbering  from  sixty  to  eighty,  so  ar- 
ranged as  to  resemble  the  disk  of  a  radiated  flower.     In  Fig. 
161  they  are  represented  as  they  appear  in  looking  at  them 
from  behind,  the  back  part  of  the  eye  being  removed.     At  1 
is  the  divided  edge  of  the  three  coats ;  2,  the  pupil ;  3,  the  iris ; 
4,  the  ciliary  processes.     At  5  is  the  anterior  edge  of  the  retina, 


292  HUMAJST  PHYSIOLOGY. 

Object  of  the  apparatus  to  form  images  of  objects  on  the  retina. 


FIG.  161. 


CILIARY   PROCESSES. 

which  stops  at  the  beginning  of  these  processes,  presenting,  as 
you  see,  a  scalloped  appearance.  The  processes,  however,  do 
not  arise  from  the  retina,  but  come  from  the  choroid  coat,  and 
are  united  at  their  origin  by  a  ring  of  ligamentous  substance 
to  the  sclerotic  coat.  The  exact  operation  of  this  beautiful 
arrangement  is  not  known,  but  it  is  pretty  well  ascertained, 
that  muscular  fibres  are  so  connected  with  these  processes,  that 
when  they  contract  they  draw  the  crystalline  lens  forward. 
This,  as  you  will  see  in  another  part  of  this  chapter,  is  a  very 
important  movement  in  the  adaptation  of  the  eye  to  seeing  at 
different  distances. 

439.  The  object  of  all  this  apparatus,  which  I  have  de- 
scribed, is  to  have  images  of  objects  formed  in  the  back  part 
of  the  eye  upon  the  retina,  so  that  the  optic  nerve  expanded 
there  may  carry  impressions  from  them  to  the  brain.  This  is 
done  in  this  way.  The  rays  of  light  coming  from  an  object 
pass  through  first  the  cornea,  then  the  aqueous  humor,  then 
the  crystalline  lens,  and  lastly  the  vitreous  humor  to  the  retina, 
where  they,  so  to  speak,  daguerreotype  the  object.  The  fact 
that  such  an  image  is  formed  has  been  often  proved  by  obser- 
vation on  the  eyes  of  animals.  If  the  eye  of  a  rabbit  be 
cleansed  from  the  fat  and  muscles  at  its  back  part,  and  a  candle, 
be  held  in  front  of  it,  you  can  see  the  image  of  the  candle 
through  the  sclerotic  coat,  formed  upon  the  retina.  So  if  you 
take  the  eye  of  an  ox,  and  carefully  pare  off  the  back  part,  so 


THE  EYE. 


293 


Images  on  the  retina  inverted.    Camera  Obscura. 


as  to  leave  it  very  thin,  a  distinct  image  of  any  thing  placed  in 
front  of  the  eye  may  be  seen  at  the  back  part.  The  image 
however  will  be  inverted,  as  represented  in  Fig.  162.  For  the 


FIG.  162. 


sake  of  clearness  two  rays  only  are  represented  as  coming  from 
each  of  the  two  ends  of  the  object,  a,  c.  These  rays  cross  each 
other  in  the  middle  of  the  eye,  those  from  a  being  brought  to 
a  focus  at  6,  and  those  from  c  at  d.  As  all  the  other  rays, 
coming  from  other  points  in  the  object,  are  refracted  in  the 
same  manner,  a  complete  inverted  picture  of  it  is  thus  formed. 
The  same  thing  is  seen  in  the  instrument  called  the  camera  ob- 
scura.  If  light  be  let  into  a  darkened  room  through  a  small 
aperture  in  a  window  shutter,  an  inverted  picture  of  objects 
without  can  be  seen  on  a  screen,  as  represented  in  Fig.  163. 

FIG.  163. 


This  experiment,  which  can  be  performed  by  any  one,  illustrates 
in  a  rude  way  the  principle  of  the  camera  obscura.  The  real 
instrument  has  a  tube  with  a  double  convex  lens,  so  as  to  collect 
together  the  rays  from  objects,  and  concentrate  them  upon  a 
small  space,  thereby  making  a  very  distinct  small  image  of 
them.  The  eye  is  a  very  beautiful  and  perfect  instrument  of 
this  sort.  The  space  filled  by  the  vitreous  humor  is  the  dark- 
ened room ;  the  pupil  answers  to  the  hole  in  the  window  shut- 

25* 


294  HUMAN   PHYSIOLOGY. 

Cornea.     Iris.    Its  radiated  and  circular  muscular  fibres. 

ter,  or  the  tube  of  the  more  perfectly  constructed  camera ;  the 
crystalline  humor  is  the  lens ;  and  the  retina  is  the  screen  on 
which  the  images  are  formed. 

We  will  now  attend  to  the  agency  which  the  different  parts 
have  in  producing  the  result,  for  which  the  apparatus  is  con- 
structed, observing  the  perfect  adaptation  of  each  of  them  to 
the  particular  part  which  it  performs  in  the  process. 

440.  The  cornea,  as  it  lets  in  the  light,  requires  to  be  trans- 
parent, and,  as  it  is  very  much  exposed  to  injury,  it  also  re- 
quires to  be  very  firm  and  hard.     Both  of  these  objects  are 
secured  in  an  admirable  manner.     Its  transparency  is  secured 
in  this  way.     It  is  made  of  different  layers,  which  are  kept 
moist  by  a  delicate  transparent  fluid.     It  is  this  which  in  health 
makes  the  eye  so  clear  and  sparkling.     Disease  often  so  lessens 
it,  as  to  give  this  window  of  the  eye  a  dull  appearance.     The 
cornea  is,  as  you  see  by  Fig.  159,  more  convex  than  the  sclerotic 
coat,  so  that  it  may  act  with  some  power  as  a  lens  in  making 
the  rays  converge. 

441.  The  iris  is  a  circular  curtain  with  a  round  opening  in 
its  centre,  the  pupil,  which  can  be  varied  in  size  to  a  consider- 
able degree.     On  the  iris  depends  ,vhat  is  called  the  color  of 
the  eye,  which  is  various,  as  blue,  nearly  black,  grey,  hazel,  &c. 
The  color  is  owing  to  the  pigment  which  is  in  cells  on  its  inner 
surface.     The  chief  office  of  the  iris  is  to  regulate  the  quantity 
of  light  that  enters  the   eye.     When  the  light  is  obscure  the 
opening  in  the  iris  is  widely  dilated ;   but  when  there  is  much 
light  it  is  contracted ;  and  if  the  light  be  excessive,  it  is  con- 
tracted almost  to  a  point.     Its  motions,  therefore,  considering 
irig  its  small  extent,  have  a  very  wide  range.     You  can  realize 
this  if  you  look  at  the  eye  of  some  one  in  a  dim  light,  and  then 
suddenly  bring  a  lighted  candle  very  near  to  it.     These  motions 
are  effected  by  a  peculiar  arrangement  of  muscular  fibres,  of 
which  the  iris  is  in  part  composed.     There  are 

two  sets  of  fibres,  the  circular  and  radiated,  as 
represented  in  Fig.  164.  When  the  circular 
fibres  contract,  the  pupil  is  contracted ;  and  when, 
on  the  other  hand,  the  radiated  fibres  contract, 
the  pupil  is  dilated.  There  must  be  a  very  nice 
adjustment  of  the  fibres,  to  enable  them  to  di- 
late the  pupil  as  widely  as  they  sometimes  do, 
without  producing  any  puckering  of  the  surface  of 
the  iris.  The  opening  in  the  iris  is  always  round  in  man  ;  but 
in  animals  whose  range  of  vision  requires  to  extend  widely  in 


THE   EYE.  295 


Crystalline  lens.     Seat  of  cataract.     Choroid  coat.     Why  dark. 

a  korizontal  direction,  (as  the  herbivorous  animals,)  it  is  in  the 
form  of  an  ellipse,  with  the  long  diameter  horizontal.  In  ani- 
mals, on  the  other  hand,  that  leap  up  and  down  in  pursuit  of 
their  food,  as  the  cat  and  other  carnivorous  animals  that  seek 
their  prey  in  the  same  manner,  the  pupil  has  the  elliptical 
form,  but  with  the  long  diameter  vertical. 

442.  The  crystalline  lens  is  the  chief  agent  in  the  eye  in  con- 
centrating the  rays  of  light  by  refraction.     In  Fig. 

165  you  have  a  side  view  of  it.     Its  anterior  part,        FIG-  165> 
1,  is  less  convex  than  its  posterior,  2.     In  Fig.  166 
is  a  magnified  view  of  the  lens  hardened  in  spirit 
and  cut  open,  so  as  to  show  the  different  layers  of 
which  it  is  formed.     The  layers  are  more  and  more 
hard  as  you  go  towards  the  centre.     The  object  of 
this  arrangement  and  of  the  peculiar  shape  of  the     Crystalline  Len«- 
lens,   is    not   as   yet    understood. 
This  lens  is  the  seat  of  the  disease  ^G-  166- 

called  cataract.  In  this  disease 
the  lens  becomes  opake  so  as  to 
prevent  the  rays  of  light  from  pass- 
ing to  the  retina.  There  are  three 
ways  of  getting  rid  of  the  difficulty. 
One  is  to  introduce  an  instrument 
shaped  like  a  needle  into  the  side 
of  the  eyeball,  with  which  the  opake 
lens  is  pushed  off  one  side  in  the 
vitreous  humor,  so  as  to  be  out  of 
the  way  of  the  rays  of  light.  An- 
other is  to  break  up  the  lens  with  the  needle,  so  that  its  frag- 
ments may  be  absorbed.  The  third  method  is  to  make  an 
opening  in  the  cornea,  and  to  extract  the  lens  through  it. 

443.  The  choroid  coat  (6,  Fig.  159)  contains  quite  a  large 
share  of  the  minute  bloodvessels,  and  nerves  of  the  eye,   and 
serves  for  a  medium  by  which  they  pass  to  other  parts  of  this 
organ.     But  it  serves  another  important  purpose  by  means  of 
its  dark  pigment.     It  makes  a  dark  chamber  of  the  back  part 
of  the  eye  where  the  optic  nerve  is  expanded.     The  object  of 
this  is  to  secure  distinctness  in  the  images   formed  upon  the 
retina.     If  the  choroid  coat  were  of  a  light  color,  there  would  be 
so  much  reflection  of  the  rays  of  light  back  and  forth  in  all 
directions  in  the  eye,  that  the  pictures  formed  upon  the  retina 
would  be  confused.     There  would  be  a  glare  of  light,  such  as 
we  experience  in  a  room  where  the  walls  are  all  of  a  very  lighl 


296  HUMAN   PHYSIOLOGY. 

Want  of  pigment  in  the  choroid  of  the  albino.    The  retina. 

color.  There  is  the  same  reason  for  having  the  chamber  of 
the  eye  of  a  dark  color,  as  for  having  that  of  the  camera  ob- 
scura  so.  In  the  albino  there  is  a  deficiency  of  the  pigment  of 
the  choroid ;  and,  therefore,  in  a  bright  light  there  is  in  his  cas( 
a  defect  of  vision,  from  the  cross  reflection  to  which  I  havt 
alluded.  During  the  day  his  vision  is  very  indistinct ;  and  it  is 
only  when  twilight  appears  that  he  can  see  well,  or  with  com- 
fort. The  pigment  is  also  deficient  in  the  iris  of  the  albino ; 
and  the  bright  red  or  pinky  hue  of  the  iris  in  his  case  is  owing 
to  the  blood  in  the  minute  bloodvessels,  with  which  this  part 
is  so  well  supplied.  Those  animals  that  use  their  eyes  mostly 
in  daylight  have  the  pigment  of  the  choroid  of  the  darkest 
color ;  while,  on  the  other  hand,  those  that  need  to  see  most 
clearly  at  night,  as  the  owl,  either  have  none  of  this  pigment, 
or  have  it  of  a  very  light  color. 

444.  The  retina  is  a  soft  greyish  delicate  membrane,  formed 
chiefly  of  the  expansion  of  the  optic  nerve.     Here  the  images 
are  formed,  and  the  minute  fibres  of  nerve  in  this  membrane 
receive  impressions  from  these  images,  which  are  transmitted  to 
the  brain  by  the  trunk  of  the  nerve.     This  nerve  has  the  same 
relation  to  light  that  the  nerve  of  hearing  has  to  sound,  the 
nerve  of  smell  to  odors,  or  the  nerve  of  touch  to  the  qualities 
of  bodies  that  we  feel.     And  it  is  curious  to  observe  that  the 
termination  of  the  nerve  of  sight  on  the  surface  of  the  retina 
is  arranged  in  papillce,  just  as  the  terminations  of  the  nerves 
of  touch  are.     In  Fig.  167  is  represented 

a  portion  of  the  retina  of  a  frog  magni-  FIG.  167. 

fied  three  hundred  times.  The  upper 
rows  of  papillae,  which  are  without  dots, 
are  seen  sideways. 

445.  The  superiority  of  the  eye,  as  an 
optical  instrument,  is  seen  in  a  striking 
manner  in  several  particulars,  in  which 
difficulties  and  defects  to  which  all  opti- 
cal instruments  are  liable  are  removed.     There  is,  for  example, 
a  defect  in  the  operation  of  lenses  in  optical  instruments,  which 
is  termed  spherical  aberration.     This  can  be  explained  on  Fig. 
168,  which  represents  a  lens,  L,  I/,  with  some  of  the  rays  as 
they  pass  through  it.     Now  the  rays  R,  R",  R'",  are  brought 
to  a  focus  at  F ;  while  the  rays  R,  L  and  R"",  L'  come  to  a 
focus  much  nearer,  at  L     It  was  found  by  experiment,  that  if  the 
central  portion  of  the  lens  be  covered,  so  that  the  rays  R',  R" 
R'",  cannot  pass,  a  distinct  image  will  be  formed  on  a  screen 


THE  EYE.  297 


Spherical  and  chromatic  aberration.    How  remedied  in  the  eye. 


B- 


put  at  I.  And,  on  the  other  hand,  if  the  outer  portion  of  the 
lens  be  covered,  so  that  the  outer  rays  are  intercepted,  then  the 
middle  rays,  R'  R"  Rr//  will  form  an  image  on  a  screen  at  F. 
But  if  the  whole  lens  be  used,  no  distinct  image  is  formed,  wher- 
ever you  may  place  the  screen.  If  you  place  it  at  /,  it  will 
receive  with  the  rays  that  come  to  a  focus  there,  rays  that  have 
their  focus  at  F.  And  so  of  other  points. 

446.  It  is  in  view  of  such  experiments,  that  a  contrivance 
has  been  adopted  in  the  construction  of  telescopes  and  micro- 
scopes, for  the  purpose  of  remedying  the  difficulty  above  de- 
scribed.    What  is  called  a  diaphragm,  or  stop,  is  put  in  against 
every  lens.     It  is  a  perforated  partition  which  permits  the  light 
to  pass  only  through  the  central  portion  of  the  lens.     The  lines 
D,  D',  in  Fig.  168,  cutting  off  all  rays  in  the  neighborhood  of 
R  and  R"",  show  the  operation  of  the  stop.     In  the  eye  the 
iris  acts  as  the  diaphragm  or  stop  to  the  crystalline  lens  which 
is  behind  it,  as  you  can  see  by  recurring  to  Fig.  159.     Ordina- 
rily, by  means  of  this  stop,  the  rays  pass  through  only  the 
central  part  of  the  lens. 

447.  Another  difficulty  attending  the  operation  of  a  common 
lens  is  what  is  termed  chromatic  aberration.     Every  ray  of  white 
light  consists  of  a  mixture  of  rays  of  seven  different  colors. 
Some  of  these  colors  are  more  easily  refracted  than  others,  and 
therefore  on  passing  through  a  lens  will  come  to  a  focus  sooner. 
This  of  course  is  apt  to  make  some  confusion  in  the  color  and 
the  distinctness  of  objects,  when  seen  through  a  single  lens,  or 
through  several  if  they  are  alike.     The  difficulty  has  been  rem- 
edied, although  Sir  Isaac  Newton  thought  that  it  never  would 
be.     And  it  is  said  that  the  hint  of  the  remedy  was  taken  from 
the  arrangement  of  the  eye.     At  any  rate,  the  defect  is  avoided 


298  HUMAN  PHYSIOLOGY. 

Adjustment  of  the  eye  to  objects  at  different  distances. 

by  having  lenses  made  of  different  materials,  just  as  is  the  case 
in  the  eye.  Thus  if  two  lenses  be  used,  one  of  which  is  made 
of  flint  and  the  other  of  common  glass,  the  difficulty  disappears. 
In  the  eye  it  is  perfectly  avoided  by  the  passage  of  the  rays 
through  so  many  different  materials,  before  it  reaches  the  retina. 
The  stop  has  been  found  a  partial  remedy  in  the  case  of  optical 
instruments ;  and  the  iris,  the  stop  of  the  eye,  of  course  acts  in 
the  same  way.  But  the  full  remedy  was  not  found,  till  another 
step  was  taken  in  imitation  of  the  eye,  the  most  perfect  of  all 
optical  instruments. 

448.  There  is  another  arrangement  in  the  eye,  which  the 
optician  can  imitate  only  in  a  comparatively  bungling  manner. 
It  is  that  by  which  the  eye  adapts  itself  to  different  distances  in 
looking  at  objects.  If  we  look  through  a  telescope  at  a  near 
object,  and  then  turn  it  towards  one  at  a  distance,  we  cannot 
see  it  distinctly  until  we  adjust  the  lenses  to  suit  the  distance. 
But  in  the  eye  how  quickly  the  adjustment  is  made !  It  is 
done  ordinarily,  without  any  effort  on  our  part  of  which  we  are 
conscious.  It  is  done  so  easily  that  we  do  not  think  of  the 
change.  We  look  at  an  object  at  a  few  inches  distance,  and  in 
an  instant  turn  the  eye  and  see  an  object  afar  off  with  almost 
equal  distinctness.  There  has  been  much  discussion  in  regard 
to  the  means  by  which  this  adjustment  is  effected.  One  of  the 
means  undoubtedly  is,  a  change  in  the  relative  position  of  the 
crystalline  lens,  which  is  effected  by  the  muscular  fibres  spoken 
of  in  §  438.  These  fibres  when  they  contract,  draw  the  lens  to- 
wards the  front  of  the  eye,  and  away  from  the  retina.  This  is 
done  whenever  we  look  at  a  near  object.  If  it  were  not,  the  rays 
which  come  from  the  object,  as  they  diverge  considerably,  would 
not  be  brought  to  a  focus  when  they  reach  the  retina.  The 
iris  also  has  some  agency  in  adjusting  the  eye  for  seeing  at 
different  distances.  When  the  eye  is  turned  to  a  near  object 
the  pupil  always  contracts,  thereby  shutting  out  those  rays 
coming  from  it  which  are  the  most  divergent. 

FIG.  169. 


THE  EYE.  299 


Difficulty  in  the  near-sighted  and  the  far-sighted. 


449.  In  some  cases  this  power  of  adjustment  is  counteracted 
by  defect  in  the  arrangement  of  the  eye.     Thus,  in  the  near- 
sighted, either  the  cornea  or  the  crystalline  lens,  or  both,  are 
too  convex ;  or,  the  crystalline  lens  is  too  far  from  the  retina. 
The  result  is,  that  the  rays  of  light  coming  from  a  distant  ob- 
ject come  to  a  focus  before  they  reach  the  retina,  as  represented 
in  Fig.  169.     All  objects,  therefore,  are  seen  indistinctly  except 
those  which  are  brought  near  to  the  eye.     This  defect  is  rem- 
edied by  the  use  of  a  concave  lens,  which  counteracts  the  effect 
of  the  too  highly  refractive  power  of  the  eye  by  making  the 
rays  divergent,  instead  of  parallel,  before  entering  the  eye.     By 
an  habitual  adjustment  of  the  eye  for  seeing  near  objects,  near- 
sightedness  may  be  produced.     Hence  it  is  that  engravers, 
watch-makers,  students,  <fec.,  are  so  liable  to  become  near  sighted. 

450.  In  the  far  sighted  the  difficulty  is  of  an  opposite  char- 
acter.    The  refractive  power  of  the  eye  is  too  feeble.     This  is 
owing  either  to  too  little  convexity  of  the  cornea,  or  of  the 
crystalline  lens,  or  of  both ;  or,  to  too  great  nearness  of  the 
crystalline  lens  to  the  retina.     In  this  case  the  rays  coming 
from  a  near  object  do  not  come  to  a  focus  soon  enough.     The 
focus  of  the  rays  coming  from  any  point  of  the  object  is  behind 
the  retina,  as  seen  in  Fig.  170,  in  which  the  rays  from  two 


FIG.  170. 


points  are  represented  as  prolonged  till  they  meet  at  their  focus 
behind  the  retina.  This  defect  is  palliated  by  the  use  of  convex 
glasses.  It  is  quite  common  in  persons  who  have  passed  middle 
age  ;  while  near-sightedness  appears  mostly  in  younger  persons, 
the  full  compliment  of  the  humors  of  the  eye  in  their  case 
making  the  front  part  of  the  organ  prominent. 

451.  There  has  been  much  discussion  of  the  question  why 
we  see  every  thing  in  its  real  position,  while  the  images  of  ob- 
jects are,  as  you  have  seen  in  §  439,  reversed  on  the  retina.  It 
has  been  supposed  by  some  that  we  really  see  every  thing  re- 
versed, and  that  our  experience  with  the  sense  of  touch,  in 
connection  with  that  of  vision,  sets  us  right  in  this  particular. 


300  HUMAN   PHYSIOLOGY. 


Why  we  see  things  erect,  though  their  images  on  the  retina  are  reversed. 


And  this,  it  is  supposed,  is  the  more  readily  done  from  the  fact, 
that  our  own  limbs  and  bodies  are  reversed  as  pictured  on  the 
retina,  as  well  as  objects  that  are  around  us,  so  that  every  thing 
is  relatively  right  in  position.  But  if  this  be  the  true  explana- 
tion, those  who  have  their  sight  restored,  after  having  been 
blind  from  birth,  should  at  first  see  every  thing  wrong  side  up, 
and  should  be  conscious  of  rectifying  the  error  by  looking  at 
their  own  limbs  and  bodies.  But  this  is  not  so.  In  the  case 
related  by  the  anatomist  Cheselden,  of  the  boy  who  was  blind 
from  birth,  and  who  at  about  the  age  of  thirteen  had  his  sight 
restored  by  an  operation,  there  was  no  complaint  that  he  did  not 
see  things  erect  at  the  first.  If  this  difficulty  had  existed,  he  would 
have  complained  of  it  quite  as  readily  as  he  did  of  the  difficulty 
in  estimating  the  size  and  the  distance  of  objects.  The  above 
explanation  of  erect  vision,  and  other  explanations  of  a  similar 
character,  are  based  upon  a  wrong  idea  of  the  office  which  the 
nerve  performs  in  the  process  of  vision.  It  is  not  the  image 
formed  upon  the  retina  which  is  transmitted  to  the  brain,  but 
an  impression  produced  by  that  image.  The  mind  does  not 
look  in  upon  the  eye  and  see  the  image,  but  it  receives  an  im- 
pression from  it  through  the  nerve ;  and  this  impression  is  so 
managed  that  the  mind  gets  the  right  idea  of  the  relative  position 
of  objects.  Of  the  way  in  which  this  is  done  we  know  as  little 
as  we  know  of  the  nature  of  the  impression  itself. 

452.  It  is  an  interesting  and  wonderful  fact,  that  as  we  look 
at  an  object  with  both  eyes,  although  there  are  two  images 
formed,  and  therefore  two  impressions  are  carried  to  the  brain 
by  the  two  nerves,  yet  a  single  impression  is  produced  in  the 

FIG.  171. 


THE  EYE.  301 


Correspondence  of  action  between  the  two  eyes. 


mind.  To  produce  this  single  effect  at  the  end  of  the  process 
of  seeing,  it  is  manifest  that  there  must  be  a  very  exact  corres- 
pondence in  the  two  eyes  as  optical  instruments.  The  two 
images  must  be  similar,  and  must  be  formed  on  corresponding 
parts  of  the  retina  in  both  eyes.  Thus,  if  there  be  a  range  of 
objects,  as  at  A,  B,  C,  in  Fig.  171,  the  impression  will  be  a 
single  one  in  the  mind,  because  the  picture  of  these  objects  is 
on  the  same  part  of  the  retina  in  both  eyes,  a,  6,  c,  and  a',  &',  cr. 
But  if  you  press  with  your  finger  one  of  the  eyes  a  little  out 
of  its  place,  all  these  objects  will  appear  double,  because  their 
images  occupy  different  parts  of  the  retina  in  the  two  eyes. 

453.  It  is  essential,  therefore,  that  the  muscles  which  move 
the  eyes,  as  we  direct  them  towards  different  objects,  should 
harmonize  in  their  action.  They  must  move  together  with 
great  exactness,  or  there  will  be  disarrangement  of  vision.  If  the 
want  of  correspondence  be  slight,  the  vision  will  be  merely 
confused.  But  if  it  be  considerable,  so  that  the  images  are 
formed  on  quite  different  parts  of  the  retina,  in  the  two  eyes, 
every  object  will  be  distinctly  double.  You  can  verify  this,  by 
pressing  one  of  your  eyes  with  the  finger  with  different  degrees 
of  force,  while  you  look  at  the  objects.  The  intoxicated  man 
often  sees  indistinctly,  and  sometimes  even  double,  from  this 
want  of  correspondence  in  the  action  of  the  muscles  moving 
the  eyes.  This  is  one  of  the  causes  of  double  vision,  as  we  see 
it  occurring  in  disease.  I  will  cite  a  case  which  has  recently 
come  under  my  care,  in  illustration.  The  patient  could  see  as 
usual,  so  long  as  he  looked  directly  in  front,  or  towards  the 
left.  But  when  he  turned  his  eyes  to  look  towards  the  right, 
he  saw  every  thing  double,  and  the  farther  he  looked  in  that 
direction,  the  farther  apart  were  the  two  images  of  every  ob- 
ject. The  reason  was  obvious.  In  looking  to  the  right,  the 
left  eye  turns  towards  the  nose,  while  the  right  eye  turns  from 
it  outward.  The  failure  in  this  case  was  in  the  action  of  the 
muscle  that  turns  the  right  eye  from  the  nose.  The  conse- 
quence was,  that  as  he  attempted  to  turn  his  eyes  to  look  to 
the  right,  the  right  eye  did  not  correspond  in  its  motion  with 
the  left,  but  remained  nearly  stationary,  presenting  therefore  a 
squinting  appearance.  In  common  squinting,  there  is  a  per- 
manent contraction  of  one  of  these  straight  muscles,  similar  to 
that  which  we  see  in  wry-neck,  as  stated  in  §  308.  When 
this  difficulty  exists,  the  images  of  objects  are  formed  in  two 
different  parts  of  the  retina  in  the  two  eyes,  as  in  the  case  which 
I  have  just  related.  We  should  therefore  expect  that  there 

26 


302  HUMAN  PHYSIOLOGY. 

The  two  images  of  an  object  in  the  two  eyes  not  always  exactly  alike. 

would  be  double  vision,  but  ordinarily  there  is  not.  Why  is 
this  ?  It  is  because  the  mind  acquires  the  habit  of  attending 
to  the  impression  that  comes  from  one  eye  alone,  the  sound  one. 
If  the  squinting  occur  suddenly  there  is  double  vision  at  first, 
because  it  takes  a  little  time  for  the  mind  to  acquire  the  habit 
referred  to.  But  it  generally  comes  on  gradually,  and  there- 
fore there  is  no  difficulty  in  the  acquisition  of  this  habit,  to 
meet  the  exigency  of  the  case. 

454.  While  it  is  necessary  to  single  vision  when  both  eyes 
are  used,  that  the  image  of  the  object  should  occupy  corres- 
ponding portions  of  the  retina  in  the  two  eyes,  it  is  not  true 
that  these  two  images  are  in  all  cases  exactly  alike.     They  are 
so  when  the  object  presents  a  plane  surface,  or  one,  every  line 
of  which  can  be  seen  equally  well  by  both  eyes.     But  if  the 
object  be  such  that  some  lines  or  surfaces  of  it  are  seen  by  one 
eye  alone,  while  other  lines  and  surfaces  of  it  are  seen  only  by 
the  other  eye,  two  different  images  are  obviously  formed  in  the 
two  eyes.     You  can  verify  this  by  a  simple   experiment.     If 
you  hold  a  book  before  your  eyes,  with  its  back  in  a  vertical 
direction,  you  see  the  back  of  the  book  and  its  sides  at  once,  as 
a  single  object.     If  now,  still  holding  the  book  in   the  same 
position,  you  shut  one  eye,  you  see  but  one  side  of  the  cover  of 
the  book — that  one  which  is  on  the   same  side  with   the  open 
eye.     And  so  with  the  other  eye.     The  plain  inference  is,  that 
when  you  look  at  the  book  with  both  eyes,  the  image  formed 
in  the  right  eye  is  composed  of  the  back  of  the  book  and  the 
cover  of  the  right  side,  while  the  image  in  the  left  eye  is  com- 
posed of  the  back  of  the  book  and  the  cover  of  the  left  side. 
From  these  two  distinct  images,  of  course,  two  distinct  impres- 
sions are  sent  to  the  brain ;  and  yet  but  a  single  impression  is 
recognized  there  by  the  mind,  for  the  book  is  seen  as  a  single 
object.     This  single  impression  must,  therefore,  result  in  some 
way  from  a  mingling  of  the  two  impressions  transmitted  along 
the  two  optic  nerves.     Were  it  not  for  this  mingling  of  the  two 
impressions,  we  should  see  double,  that  is,  see  two  things,  when- 
ever we  look   at  any  solid  projecting  object,  and  should  see 
single  only  when  we  look  at  plane  surfaces.     Indeed,  one  who 
has  but  one  eye  can  not  acquire  from  sight  alone  any  idea  of 
solidity.     Every  thing  would  appear  to  him  to  be  on  a  plane 
surface,  till  he  finds  it  to  be  otherwise  by  the  use  of  the  sense 
of  touch,  in  connection  with  that  of  sight. 

455.  The  statements  in  the  last  paragraph  are  beautifully 
illustrated  by  the  instrument  contrived  by  Professor  Wheatstone, 


THE  EYE. 


303 


Explanation  of  the  stereoscope. 


which  he  calls  the  stereoscope.  In  using  this  instrument,  you 
look  at  two  pictures  of  the  same  object  with  the  two  eyes,  and 
yet  you  see  but  one  thing — that  is,  but  one  impression  is  pro- 
duced in  the  mind,  although  two  different  pictures  are  made  in 
the  two  eyes,  and  of  course  two  different  impressions  are  con- 
veyed to  the  brain.  Suppose  the  object  represented  is  a  book, 
as  described  in  the  experiment  alluded  to,  in  §  454.  In  the 
right  half  of  the  instrument  is  a  representation  of  the  book,  as 
seen  by  the  right  eye,  and  in  the  left  half  is  a  representation  of 
it  as  seen  by  the  left  eye.  As  you  look  at  them  you  see  but 
one  book,  just  as  you  do  in  holding  the  book  before  your  eyes. 
The  two  different  images  formed  in  the  two  eyes  are  the  same 
in  the  two  experiments.  The  same  thing  is  done  with  other 
objects.  Thus,  the  two  representations  of  a  dog,  seen  in  Fig. 
172,  are  seen  in  the  instrument  as  a  single  dog.  You  observe 

FIG.  172. 


that  they  are  shaded  differently.  They  are  representations  of 
the  two  pictures,  which  a  dog  in  this  position  would  make  on 
the  retina  in  both  of  the  eyes  of  a  person  looking  at  him. 
When  you  look  at  them  in  the  instrument,  the  single  dog  that 
you  see  stands  out  more  than  either  of  the  two  representations, 
as  seen  when  they  are  not  in  the  instrument.  The  reason  is 
obvious.  In  the  two, images  formed  in  the  eyes,  as  you  look 
into  the  instrument,  are  all  the  lines  of  light  and  shade,  which 


304 


HUMAN  PHYSIOLOGY. 


Rude  imitation  of  the  stereoscope. 


you  would  see  in  looking  at  a  real  dog  with  both  eyes ;  while 
either  one  of  these  representations  contains  only  a  part  of  these 
lines.  You  can  imitate  in  some  good  degree  the  effect  of  the 
stereoscope,  by  placing  the  end  of  a  small  book  between  these 
figures,  and  letting  the  other  end  rest  against  the  nose  and  fore- 
head, thus  separating  the  eyes  from  each  other.  If  now  you 
look  intently  at  the  two  figures,  you  will  in  a  few  moments  find 
them  approximate  each  other,  till  at  length  they  mingle  to- 
gether, and  you  will  see  but  a  single  dog  standing  out  like  a 
statue.  The  same  thing  can  be  shown  by  mathematical  figures. 
Thus,  if  two  figures  a  a,  represented  in  Fig.  17$,  be  placed  in 

FIG.  173. 


\ 


\ 
/ 

I 

/ 
\ 

the  two  apartments  of  the  instrument,  on  looking  into  it  you 
will  see  a  single  figure,  shaped  like  b.  You  can  imitate  the 
stereoscope  here  also,  by  placing  the  end  of  a  book  in  such  a 
way  as  to  cover  the  middle  figure,  the  other  end  being  between 
the  eyes.  The  two  figures  will  run  together,  and  the  union 
will  represent  the  figure  of  a  truncated,  four-sided  figure,  stand- 
ing out  in  bold  relief.  But  such  experiments  afford  only  a  rude 
imitation  of  the  stereoscope,  for  in  this  instrument  the  separa- 
tion between  the  eyes  is  entire,  so  that  the  effect  is  produced 
at  once.  There  is  no  running  together  of  the  two  figures,  but 
the  moment  that  you  look  into  the  instrument  they  are  blended 
in  one. 

456.  The  harmony  which  we  have  seen  to  exist  in  the  action 
of  the  eyes  is  very  wonderful.  It  must  be  remembered  the.t 
the  eyes  are  optical  instruments,  endowed  with  self-adjusting 
powers,  to  accommodate  the  different  distances  of  objects,  and 
the  varying  degrees  of  light.  And  thus  must  both  be  just 
alike  in  all  these  diversified  adjustments,  that  the  images  in 
both  may  correspond.  And  besides  all  this  adjusting  machinery 
inside  of  the  eyes,  so  delicate  and  so  correspondent  in  its  action 
in  both,  there  is  muscular  machinery  outside,  to  move  the  eye- 


THE  EYE.  305 


Correspondence  not  only  between  the  two  eyes,  but  also  between  their  nerves. 

balls  in  all  directions ;  and  in  these  movements  also,  as  you 
have  seen,  there  is  an  exact  correspondence.  All  these  motions 
for  adjusting  this  complicated  machinery  within  and  around  the 
eyes,  are  regulated  by  the  nerves.  How  astonishing  the  accu- 
racy with  which  they  do  this !  How  exact  are  the  different 
impressions  transmitted  through  them,  in  producing  the  various 
degrees,  and  multiplied  combinations  of  action,  in  the  little 
muscles  of  these  organs ! 

457.  There  is  correspondence  not  only  in  the  machinery  of 
the  eyes,  as  optical  instruments,  but  also  in  that  portion  of  the 
process  of  seeing  which  is  not  mechanical.     The  nerves  of  vis- 
ion must  be  exactly  correspondent  in  the  two  eyes,  that  similar 
impressions  may  go  from  the  retina  to  the  brain  in  both.     And 
the  correspondence  is  in  this  case  the  more  wonderful  from  the 
fact,  that  the  impressions  transmitted  are,  as  you  have  seen, 
not  always  precisely  alike.     How  the  harmony  is  preserved  in 
connection  with   this  variation  is  a  great  mystery.     We  can 
readily  conceive  how  a  single  impression  can  result  in  the  mind, 
from  two  impressions  transmitted  to  the  brain  from  two  images 
which  are  exactly  alike.     But  we  cannot  conceive  how  confu- 
sion can  be  avoided  when  the  images  and  the  consequent  impres- 
sions are  in  some  measure  different.     In  this  connection  I  will 
notice  a  peculiarity  in  the  arrangement  of  the  optic  nerves. 
They  are  not  entirely  separate  as  they  go  from  the  eyes  to  the 
brain.     At  one  point  in  their  course  they  unite  together,  and 
then  separate  again.     In  doing  so,  some  fibres  from  both  the 
nerves  communicate  together,  and  some  cross  each  other,  so 
that  a  portion  of  each  nerve  passes  over  to  the  other  before 
they  go  to  the  brain.     Undoubtedly  this  arrangement  has  some 
reference  to  the  harmony  of  action  of  the  two  nerves,  but  we 
know  nothing  of  the  way  in  which  it  exercises  its  agency  in 
this  respect. 

458.  The  power  of  perceiving  the  size,  distance,  and  figure  of 
objects,  is  wholly  an  acquired  power.     The  case  already  referred 
to,  in  which  Cheselden  restored  the  sight  by  an  operation,  shows 
this  to  be  true.     "  When  he  first  saw,"  says  Cheselden  of  his 
patient,  "  he  was  so  far  from  making  any  judgment  about  dis- 
tances, that  he  thought  that  all  objects  whatever  touched  his 
eyes  (as  he  expressed  it,)  as  what  he  felt  did  his  skin,  and 
thought  no  objects  so  agreeable  as  those  which  were  smooth 
and  regular,  though  he  could  form  no  judgment  of  their  shape, 
or  guess  what  it  was  in  any  object  that  was  pleasing  to  him. 
He  knew  not  the  shape  of  any  thing,  nor  any  one  thing  froxn 

26* 


306  HUMAN  PHYSIOLOGY. 

Power  of  perceiving  the  size,  distance,  and  figure  of  objects  acquired. 

another,  however  different  in  shape  or  magnitude;  but  upon 
being  told  what  things  were,  whose  form  he  before  knew  from 
feeling,  he  would  carefully  observe,  that  he  might  know  them 
again ;  but  having  too  many  objects  to  learn  at  once,  he  forgot 
many  of  them ;  and  (as  he  said),  at  first  he  learned  to  know, 
and  again  forgot  a  thousand  things  in  a  day.  At  first  he  could 
bear  but  very  little  light,  and  the  things  he  saw  he  thought 
extremely  large ;  but  upon  seeing  things  larger,  those  first  seen 
he  conceived  less,  never  being  able  to  imagine  any  lines  beyond 
the  bounds  that  he  saw ;  the  room  he  was  in,  he  said,  he  knew 
to  be  but  part  of  the  house,  yet  he  could  not  conceive  that  the 
whole  house  could  look  bigger."  Every  infant,  if  it  could  ex- 
press its  ideas,  could  give  us  a  narrative  of  a  similar  experience, 
in  its  first  lessons  in  seeing.  It  is  obvious  that  seeing  is  a  pro- 
cess which  we  learn  to  do,  as  really  as  we  learn  to  talk  or  walk. 
The  confused  vision  of  the  infant  bears  the  same  relation  to 
the  accurate  vision  of  the  adult,  that  its  uncouth  noises  and 
awkward  motions  bear  to  the  adult's  harmonious  utterances  and 
graceful  movements.  In  order  to  acquire  definite  and  correct 
ideas  of  objects,  we  are  obliged  to  learn  how  to  use  those  opti- 
cal instruments,  the.  eyes.  The  infant  manifestly  does  not  know 
how  to  use  them  to  any  great  advantage.  He  does  not  at  first 
know  how  to  use  the  muscles  that  direct  the  eyes  towards  any 
object,  and  there  is,  therefore,  an  obvious  awkwardness  in  their 
movements.  As  he  reaches  out  his  hands  towards  objects,  it 
is  plain  that  he  does  not  appreciate  their  distances.  He  reaches 
out  for  the  moon,  or  any  other  distant  object,  just  as  he  does 
for  the  toy  that  is  held  before  him.  It  is  by  a  continued  com- 
parison of  experiences  that  he  learns  the  sizes,  shapes,  and  dis- 
tances of  objects.  And  in  doing  this,  the  sense  of  touch  acts 
as  the  educator  of  the  vision,  very  much,  as  the  ear  educates  the 
voice.  And  even  the  adult,  with  all  the  training  wmch  he  has 
bestowed  upon  his  eyes,  often  makes  mistakes,  especially  in  rela- 
tion to  magnitude  and  distance.  There  are  various  degrees  ot* 
skill  in  seeing;  and  he  is  the  most  skillful  seer  wno  makes  the 
fewest  of  the  mistakes  referred  to. 

459.  Let  us  look  now  at  the  means  by  which  we  gain  the 
experience  that  is  necessary  to  correct  vision.  One  means  is 
the  appreciation  of  the  space  occupied  by  objects  in  the  field 
of  vision.  This  is  measured  by  what  is  termed  the  visual 
angle — that  is,  the  angle  which  is  formed  by  two  lines  corning 
from  the  extremities  of  an  object,  and  meeting  in  the  eye,  as 
represented  in  Fig.  1 74.  In  this  way  we  get  the  idea  of  mag- 


THE   EYE.  307 


Visual  angle.    Distance  of  objects  estimated  by  their  distinctness. 


FIG.   174. 


nitude.  But  it  is  manifest  that  it  cannot  alone  give  us  this  idei 
correctly.  It  would  do  so,  if  all  objects  were  at  an  equa\ 
distance  from  the  eye.  But  you  can  see  by  the  figure,  that  if 
they  are  at  different  distances,  you  must  know  something  of 
those  distances,  to  estimate  the  magnitude  of  the  objects  by 
the  visual  angle,  which  they  subtend.  The  arrow  at  A,  B  will 
appear  just  as  large  as  the  larger  one  at  A',  B',  because  it  will 
occupy  the  same  space  a,  b  on  the  retina,  and  subtend  the  same 
angle.  But  if  you  know  that  the  one  is  nearer  to  you  than 
the  other,  you  make  allowance  for  this  in  the  estimation  of  the 
size.  Your  hand,  held  up  to  keep  the  rays  of  the  sun  from 
your  eyes,  would  look  to  you  as  large  as  the  sun  itself,  if  you 
did  not  know  how  near  it  is  to  you ;  and  the  sun  and  moon 
appear  to  us  to  have  about  the  same  magnitude,  because  we  do 
not  keep  in  mind  the  fact  that  the  sun  is  ninety-six  millions  of 
miles  from  us,  while  the  moon  is  only  two  hundred  and  forty 
thousand. 

460.  Another  means  which  we  use  in  getting  a  correct  idea 
of  objects  by  vision,  is  the  degree  of  distinctness  in  their  lines, 
and  shadows,  and  colors.     The  fact  is  learned  very  early  by 
the  child,  that  the  nearer  objects  are,  the  greater  is  their  dis- 
tinctness ;  and  he  makes  use  of  this  fact  continually  in  estim- 
ating both  their  distance  and  their  magnitude.     He  estimates 
the  latter  less  directly  than  he  does  the  former  by  this  means. 
He  makes  use  of  his  notion  of  the  distance  of  an  object,  gained 
by  its  degree  of  distinctness,  in  forming  an  idea  of  its  magni- 
tude.    Many  mistakes  are  made  in   the  use  of  this  means  of 
judging  of  objects.     Thus,  a  very  bright  light  will  often  appear 
to  be  nearer  than  one  that  is  less  bright.     When  the  atmos- 
phere is  very  clear,  mountains  and  other  objects  appear  nearer 
to  us  than  they  do  when  the  atmosphere  is  thick  and  hazy. 

461.  Another  means  of  making  a  correct  estimate  of  the 
distance  and  magnitude  of  objects  is,  comparison  with  other 


308  HUMAN  PHYSIOLOGY. 

Size  of  objects  estimated  by  comparison.    Muscular  sense  in  the  eye. 

objects  which  are  familiar  to  us.  Thus,  we  get  our  ideas  of 
the  size  of  animals  from  objects  in  their  neighborhood.  The 
artist  makes  use  of  this  means  of  communicating  ideas  of  size 
in  pictures  and  engravings.  Figures  of  men  are  placed  near 
large  buildings  for  this  purpose.  A  notion  of  the  great  size  of 
the  elephant  is  given  by  placing  his  keeper  at  his  side.  I  need 
not  multiply  instances  of  this  sort.  We  are  not  ordinarily 
aware  how  dependent  we  are  upon  such  comparisons,  in  esti- 
mating the  magnitude  of  objects.  An  occasional  mistake  re- 
minds us  of  it  however.  For  example,  I  once  turned  my  eye 
suddenly  from  a  giddy  height,  upon  some  huts  below  at  a  river's 
side ;  they  appeared  to  me  to  be  dog  kennels,  till  a  man  issued 
from  the  door  of  one  of  them,  and  thus  dispelled  the  illusion, 
by  affording  me  a  means  of  comparison.  So  complete  was  the 
illusion,  and  so  sudden  was  the  dissipation  of  it,  that  it  seemed 
as  if  there  was  an  instantaneous  swelling  of  dog  kennels  into 
huts.  Every  one  must  have  noticed  how  large  the  full  moon 
appears  as  he  sees  it  rising,  while  the  higher  it  rises  the  smaller 
it  becomes  to  the  eye,  although  it  is  really  at  no  greater  distance 
than  it  was  when  it  first  rose.  The  reason  is,  that  when  it  first 
rises  you  see  it  in  a  range  with  other  objects,  with  which  you 
instinctively  compare  it.  And,  therefore,  it  appears  larger  when 
you  see  it  rising  in  the  direction  of  some  distinct  object,  as  a 
large  building,  or  a  high  hill,  than  it  does  when  you  see  it  rising 
over  a  level  plain. 

462.  Another  means  of  judging  of  the  magnitude  and  dis- 
tance of  objects  is,  the  muscular  sense  (§  323)  exercised  in 
adjusting  the  eyes  in  seeing  them.  Thus,  consciousness  of 
the  amount  of  muscular  action,  in  passing  the  eye  up  and  down 
a  tall  object,  helps  to  give  us  an  idea  of  its  height.  So  too,  in 
looking  at  near  objects,  consciousness  of  the  amount  of  effort, 
in  turning  the  two  eyes  towards  the  point  looked  at,  helps  us 
to  estimate  the  distance  of  the  object.  Commonly  we  do  not 
distinctly  think  of  this  effort,  because  it  is  so  easily  made ;  but, 
if  after  looking  at  an  object  held  at  some  distance  from  the  eyes, 
we  suddenly  bring  it  very  near,  the  effort  to  make  the  axes*  of 
the  eyes  converge  enough  to  see  it  distinctly  is  very  manifest, 
producing  a  straining  effect,  which,  if  it  be  repeated  many  times 
successively,  wearies  the  eyes.  You  can  discover  how  very 
dependent  you  are  upon  this  sense  of  the  convergence  of  the 

*  The  axis  (plural  axes)  of  the  eye  is  a  line  drawn  through  the  centre  of  the  cornea 
and  pupil  backward  through  the  eye  to  the  central  point  of  the  retina.  In  Fig.  171  UM 
axes  are  B  b,  and  B  b' 


THE   EYE.  309 


Seeing  is  in  part  a  mental  process.     Really  complicated  and  difficult. 

eyes,  in  accurately  estimating  comparative  distances  in  near 
objects,  by  attempting  to  thread  a  needle,  or  nib  a  pen,  or 
snuff  a  candle  with  one  eye  shut.  The  change  in  the  converg- 
ence of  the  eyes,  on  looking  at  objects  at  different  distances,  is 
very  manifest  to  us  when  we  observe  the  eyes  of  others.  We 
perceive  thus  not  only  the  direction,  but  the  distance  of  the  objects 
at  which  they  are  looking.  We  do  this  so  continually  from  our 
infancy,  that  we  very  early  acquire  great  accuracy  in  judging, 
at  what  distance  the  point  is  towards  which  the  eyes  are  turned, 
or  in  which,  in  other  words,  the  axes  of  the  eyes  meet. 

463.  From  the  facts  presented  in  the  few  last  paragraphs,  it 
is  obvious  that  what  we  include  in  the  word  seeing  is,  to  a  great 
extent,  a  mental  process.     That  is,  there  are  certain  mental 
efforts  which  are  absolutely  essential  to  correctness  in  vision. 
Without  these  mental  efforts  or  processes,  we  could  not  see 
things  as  they  are,  as  it  is  expressed  very  properly,  but  we 
should  see  them  as  the  boy  operated  upon  by  Cheselden  did, 
when  he  first  began  to  see.     Seeing  is  cojnmonly  supposed  to 
be  a  very  simple  process.     The  idea  is,  that  one  has  merely  to 
open  his  eyes,  and  he  sees.     But,  as  you  have  seen,  the  whole 
process  is  both  a  complicated  and  a  difficult  one;  and  in  order 
to  be  able  to  do  it,  the  eyes  have  to  go  through   a  course  of 
training  in  the  case  of  every  infant,  just  as  was  the  case  with 
the  boy  whose  sight  Cheselden  restored.     We  should  be  con- 
scious of  this,  if  we  could  recollect  the  experiences  of  infancy. 
But  not  being  able  to  do  this,  it  is  only  when  we  make  some 
extraordinary  effort  in  vision,  that  we  are  at  all  sensible  that 
there  is  any  acquired  skill  in  the  process.     After  the  training 
which  the  eyes  have  in  infancy,  ordinary  seeing  is  done  with 
so  much  facility,  that  we  are  not  conscious  of  any  effort  either 
bodily  or  mental.     This  appears  very  wonderful,  when  we  con- 
sider that  the  eyes  are  two  optical  instruments,  which  need,  as 
you  have  seen,  a  most  careful  and  nice  change  of  adjustment 
continually,  to  see  in  different  directions,  and  at  different  dis- 
tances, and  that  there  is  also  considerable  and  complex  mental 
effort  in  getting  the  right  impressions  from  the  objects  which 
are  pictured  upon  the  retina. 

464.  But  there  is  another  view  in  which  the  mental  part  of 
the  process  of  vision  appears  strikingly  prominent.     When  it  is 
said  that  images  of  objects  are  formed  upon  the  retina,  and  that 
impressions  are  transmitted  from  them  to  the  brain,  this  is  far 
from  stating  all  that  is  true  on  that  point.      Many  of  the 
images  pictured  upon  the  retina  do  not  transmit  impressions  to 


310  HUMAN   PHYSIOLOGY. 

All  images  on  the  retina  do  not  produce  impressions  in  the  mind. 


the  mind.  The  sensation  of  seeing  is,  therefore,  in  relation  to 
them  incomplete — the  beginning  only  of  the  process  is  effected. 
This  you  have  seen  to  be  true  in  the  case  of  strabismus  or 
squinting.  The  faulty  eye  in  this  case  is  not  used — the  mind 
takes  no  cognizance  of  the  images  formed  in  it  (§  453).  But 
it  is  true  of  ordinary  vision  also,  that  the  mind  takes  no  cogni- 
zance of  many  of  the  images  formed  on  the  retina.  This  can 
be  verified  by  a  simple  experiment.  If  you  hold  a  finger  near 
the  eyes  (at  some  ten  or  twelve  inches  from  them),  and  a  fin- 
ger of  the  other  hand  at  a  greater  distance,  but  in  the  same 
direction,  and  then  look  at  the  near  finger,  you  will  perceive 
that  the  other  finger  appears  double.  So,  on  the  other  hand, 
if  you  look  at  the  distant  finger,  the  near  one  appears  double. 
The  reason  of  this  can  be  made  clear  to  you  by  Fig.  175.  The 
two  eyes,  L  and  R,  being  direct- 
ed so  that  their  axes  converge  FIG-  175> 
on  the  object  A,  the  middle 
points  of  the  two  wages  cor- 
respond with  the  middle  points 
of  the  retina  in  the  two  eyes,  a 
and  a'.  The  images  thus  cor- 
responding in  their  place  on  the 
retina,  the  impressions  carried 
from  them  by  the  two  optic 
nerves  to  the  brain  correspond 
also,  and  so  the  vision  is  single. 
But  the  image  of  the  object  B 
is  formed  in  the  two  eyes,  in 
parts  of  the  retina  that  do  not 
correspond,  b  and  b'.  They  are 
both  on  the  inside  of  the  mid- 
dle points,  a  a1,  that  is  towards 
the  nose;  whereas  the  outward 
part  of  the  retina  in  one  eye 
corresponds  with  the  inward 

part  in  the  other  eye,  and  vice  versa.  This  you  will  see  to  be 
true  by  recurring  to  Fig.  171,  in  which  is  shown  the  way  in 
which  a  row  of  objects  is  pictured  on  the  retina  in  the  two 
eyes.  There  you  see  that  the  image  of  the  object  A,  for  ex- 
ample, is  in  the  left  eye,  L,  on  the  inner  side  of  the  middle  point, 
b  of  the  retina;  while  in  the  right  eye,  R,  it  is  at  the  outer  side 
of  the  middle  point,  b'.  In  the  case  of  the  object  B,  then,  in  Fig. 
175,  it  is  clear  to  you  that  the  images  of  it  in  the  two  eyes  are- 


THE   EYE.  311 


Some  of  the  images  on  the  retina  are  not  attended  by  the  mind. 


formed  in  parts  of  the  retina  that  do  not  correspond,  and  there- 
fore it  appears  double. 

465,  The  application  of  all   this  to  the  point  in  hand  you 
can  readily  see.     As  the  images  of  all  objects  in  the  field  of 
vision  of  the  two  eyes  are  pictured  on  the  retina,  it  is  plain, 
according  to  the  facts  developed  above,  that  whenever  the  eyes 
are  directed   together  to  any  one  object,  other  objects  in  the 
same  direction,  but  at  a  different  distance,  must  make  images 
on  the  retina  in  the  two  eyes  that  do  riot  correspond.     We  are 
therefore  continually  seeing  double,  so  far  as  that  part  of  the 
process  of  seeing,  which  consists  in  the  formation  of  the  im- 
ages, is  concerned.     But  we  are  not  ordinarily  conscious  of 
seeing  double.     How  is  this  ?     How  is  the  difficulty  (for  it  is  a 
real  difficulty  in  the  eyes,  as  a  pair  of  optical  instruments,  aris- 
ing from  the  non-corresponding  images)  remedied  ?     It  is  dona 
obviously  in  the  other  part  of  the  process  of  seeing,  the  mental 
part.     The  mind  regulates  vision  by  the  varying  degrees  of 
attention  it  bestows  on  objects.     Ordinarily  it  does  not  attend 
to  non-corresponding  impressions  that  come  from  the  non-cor- 
responding images,  but  it  attends  only  to  those  which  are  corres- 
pondent.    As  in  squinting,  it  disregards,  as  you  have  seen,  the 
impressions  that  come  from  the  faulty  eye,  so  in  ordinary  vision 
it  disregards   many  of  the  impressions  that  come  from  both  of 
the  eyes.    By  an  effort  of  the  will  it  can  attend  to  the  impressions 
which  it  ordinarily  disregards.     When  this  effort  is  not  made, 
it  disregards  them,  as  we  may  say,  instinctively.     To  make  this 
obvious,  I  will  recur  to  the  experiment  with  the  two  fingers, 
held  at  different  distances.     WThen  you  first  attempt  the  experi- 
ment, you  do  not  for  the  moment  perceive   that  you  see  one 
finger  double,  because  you  change  the  direction  of  your  eyes 
from  one  finger  to  the  other,  so  easily  and  so  unconsciously, 
that  you  seem  to  see  them  both  singly  at  once.     But  by  a  little 
mental  effort  you  fix  your  eyes  on  one,  at  the  same  tim«  attend- 
ing to  the  images  and  consequent  impressions  produced  by  the 
other,  and  then  the  experiment  succeeds.     From  all  this  it  is 
obvious  that  the  reason  that  you  do  not  see  very  near  objects 
double,  when  looking  beyond  them  to  distant  ones,  or  see  distant 
ones  double  when  looking  at  near  ones  in  the  same  direction, 
is  simply  that  the  mind  ordinarily  attends  only  to  those  images 
and  impressions  which  are  correspondent,  while  it  with  an  ha- 
bitual instinct  disregards  those  which  are  not  so. 

466.  In  connection  with  this  subject  of  the  influence  of  mental 
attention  on  vision,  it  is  proper  to  notice  the  fact,  that  vision  is  most 


312  HUMAN   PHYSIOLOGY. 

Point  of  distinct  vision.     Minuteness  of  the  images  on  the  retina. 

distinct  at  the  central  part  of  the  retina — that  part  where  the  axis 
of  the  eye  strikes,  as  seen  in  Fig.  171,  b,  b'.  This  is  commonly 
called  the  point  of  distinct  vision.  The  mental  attention  makes 
use  of  this  point  continually.  Thus,  if  we  are  looking  intently 
at  a  minute  object,  the  eyes  are  so  directed,  that  their  converg- 
ing axes  meet  on  the  object.  So  when  we  are  reading,  although 
the  whole  page  may  be  pictured  on  the  retina  of  each  eye,  only 
the  letter  on  which  the  axes  of  the  eyes  meet  is  seen  with  per- 
fect distinctness.  And  the  point  of  union  of  the  axes  moves 
from  one  letter  to  another  along  the  lines,  so  that  each  letter  is 
successively  pictured  on  the  central  part  of  the  retina.  The 
process  is  so  rapid  that  we  are  not  conscious  of  it,  until 
we  take  pains  to  observe  what  the  process  is.  So,  in  looking 
at  a  prospect,  the  eyes  at  each  moment  see  some  one  point 
more  distinctly  than  any  other  part  of  all  that  fills  the  field  of  vis- 
ion. We  are  unconscious  of  this,  just  as  in  the  case  of  read- 
ing, because  the  axes  of  the  eyes  are  so  continually  moved  by  a 
slight  but  exceedingly  quick  motion  from  one  point  to  another. 
We  in  this  way  take  into  the  central  part  of  the  retina  so  many 
points  with  such  rapidity,  that,  by  a  mingling  of  the  impres- 
sions upon  the  mind,  we  seem  to  see  the  whole  prospect  at  the 
same  moment,  with  nearly  equal  distinctness.  The  successive 
impressions  from  the  images  on  the  retina,  occupy  so  little  time, 
that  they  appear  to  be  simultaneous,  unless  we  watch  the  process. 
467.  But  although  some  one  letter  on  a  page,  or  some  one 
point  in  a  prospect,  is  at  each  moment  seen  with  much  more 
distinctness  than  what  is  all  about  it,  yet  there  is  some  vision 
of  the  page  and  of  the  prospect  as  a  whole,  of  course  being 
less  distinct  the  farther  it  is  from  the  central  point.  It  is  pic- 
tured as  a  whole  on  the  retina,  and  the  impression  from  it  as  a 
whole  goes  by  the  nerve  to  the  brain.  The  picture  is  a  very 
minute  one,  as  it  occupies  a  small  space,  and  yet  it  is  very  dis- 
tinct in  all  its  lines,  and  shades,  and  colorings.  On  this  point 
Dr.  Paley  remarks  that  "  in  considering  vision  as  achieved  by 
the  means  of  an  image  formed  at  ',he  bottom  of  the  eye,  we 
can  never  reflect  without  wonder  upon  the  smallness,  yet  correct- 
ness of  the  picture,  the  subtility  of  the  touch,  the  fineness  of 
the  lines.  A  landscape  of  five  or  six  square  leagues  is  brought 
into  a  space  of  half  an  inch  diameter ;  yet  the  multitude  of 
objects  which  it  contains  are  all  preserved ;  are  all  discriminated 
in  their  magnitudes,  positions,  figures,  colors.  The  prospect 
from  Hampstead  Hill  is  compressed  into  the  compass  of  a  six- 
pence, yet  is  circumstantially  represented." 


THE   EYE.  313 


Our  judgment  of  the  motion  of  objects  often  erroneous. 


468.  We  form  a  judgment  of  the  motion  of  bodies,  in  part 
by  the  movement  of  the  images  of  them  upon  the  retina.     The 
perception  of  this  movement  must  be  exceedingly  delicate,  for 
even  when  a  body  passes  over  a  considerable  space,  its  image 
moves  over  a  very  small  space  on  the  retina.     "A  stage-coach," 
says   Dr.  Paley,  "traveling  at  its   ordinary  speed  for  half  an 
hour,  passes  in  the  eye  only  over  one-twelfth  of  an  inch,  yet  is 
this  change  of  place  in  the  image  distinctly  perceived  through- 
out the  whole  progress ;   for  it  is  only  by  means  of  that  per- 
ception that  the  motion  of  the  coach  itself  is  made  sensible  to 
the  eye.     If  any  thing  can  abate  our  admiration  of  the  small- 
ness  of  this  visual  tablet,  compared  with  the  extent  of  vision, 
it  is  the  reflection  which  the  view  of  nature  leads  us  every  hour 
to  make,  viz  :  that  in  the  hands  of  the  Creator,  great  and  little 
are  nothing." 

469.  Many  of  our  impressions  in  regard  to  motion,  as  we 
look  at  objects,  are  erroneous.     When  we  are  moving  ourselves, 
for  example,  stationary  objects  appear  to  move.     As  we  ride 
rapidly,  the  objects  that  we  see  seem   to  fly  by  us.     This  is 
especially  the  case,  if  the  motion  to  which  we  are  subjected  be 
an  even  one,  as  when  we  ride  in  a  rail-road  car.     And  if  we 
look  at  distant  and  near  objects  at  the  same  time,  while  the 
near  objects  seem  to  fly  back,  the  distant  seem  to  go  along  with 
us.     This  is  owing  to  their  relative  change  of  position,  as  can 
be  made  clear  by  Fig.  176.     Suppose  that  when  at  a  you  see 

FIG.  176. 


27 


314  HUMAN  PHYSIOLOGY. 

Rapidity  of  succession  of  images  on  the  retina.    How  measured. 

two  objects,  c  and  d,  in  the  same  direction.  If  you  pass  rap- 
idly to  6,  the  object  c  appears  to  have  moved  backward  in  rela- 
tion to  the  object,  d,  while  the  object,  d,  appears  to  have  moved 
forward  in  relation  to  c  ;  and  the  line,  d,  e,  represents  the  rela- 
tive change  of  positions  in  the  images  of  the  two  objects  upon 
the  retina. 

470.  As  every  object  that  we  see  is  daguerreotyped,  as  we 
may  say,  upon  the  retina,  the  rapidity  with  which  these  pic- 
tures change,  and  the  distinctness  with  which  the  nerves  trans- 
mit impressions  from  them  to  the  brain,  are  very  wonderful. 
The  time  required  for  each  transmission  is  very  small — only  the 
fraction  of  a  second.  The  length  of  time  has  been  estimated 
by  experiment.  Thus,  if  it  is  found  that  a  burning  coal,  whirl- 
ing around  at  the  rate  of  six  times  in  a  second,  produces  a 
continuous  circle  of  light,  but  that  the  circle  is  broken  when  it 
whirls  round  only  five  times  in  a  second,  we  know  that  the 
length  of  time  required  for  a  distinct  and  separate  impression 
is  the  one-fifth  of  a  second.  The  same  experiment  can  be 
tried  with  a  wheel.  In  this  case  we  observe  what  is  the  largest 
number  of  revolutions  in  a  second,  that  can  be  made  without 
blending  the  visual  impressions  of  the  spokes  into  one  con- 
tinuous impression.  By  such  experiments,  it  has  been  found 
that  the  time  required  for  a  distinct  visual  impression  varies  in 
different  individuals,  and  in  the  same  individual  at  different 
times,  from  one-fourth  to  one-tenth  of  a  second.  This  differ- 
ence in  the  rapidity  of  succession  of  the  impressions  is  of  course 
not  owing  to  any  difference  in  the  rapidity  of  the  formation  of 
the  images ;  for  they  are  formed  by  the  light,  and  light  always 
moves  with  the  same  velocity.  It  must  be  owing  manifestly  to 
a  difference  of  facility  on  the  part  of  the  mind,  in  receiving 
impressions  from  the  images.  In  other  words,  the  mental  ac- 
tivity in  the  use  of  the  optical  instruments,  the  eyes,  differs  in 
different  individuals,  and  in  the  same  individual  at  different 
times.  If  one  sees  more  quickly  than  another,  it  is  a  mental 
quickness.  It  is  a  difference  analogous  to  that  which  we  see  in 
relation  to  the  use  of  other  instruments  of  the  mind,  the  mus- 
cles for  example.  Some  use  these  instruments  much  more 
readily  and  rapidly  than  others.  We  see  this  in  the  motions 
of  the  eyes  themselves,  and  the  eyelids  also.  Some  wink  more 
quickly  than  others,  and  there  was  wisdom  in  the  decision  of 
the  blacksmith  who  dismissed  a  workman,  because  he  did  not 
wink  quick  enough,  and  was  therefore  always  getting  sparks  in 
his  eyes. 


THE  EYE.  315 


Thaumatrope.    Defenses  of  the  eye.    Bones.    Cushion  of  fat. 

471.  The  blending  of  impressions  in  vision,  produced  by 
rapid  motion,  has  been  made  use  of  in  the  contrivance  of  an 
amusing  optical  toy,  called  the  Thaumatrope.  In  making  this, 
you  cut  a  circular  card,  and  make  two  different  figures  on  its 
two  sides.  If  you  attach  two  silken  strings  to  opposite  points 
in  its  diameter,  and  then  twist  the  strings,  so  that  when  the 
card  is  left  to  go  free,  it  will  revolve  with  considerable  rapidity, 
the  two  figures  will  be  mingled  together  as  seen  by  the  eye. 
In  Figs.  177  and  178,  are  represented  the  two  sides  of  a  card, 

FIG.  177.  FIG.   178. 


prepared  in  this  way.  In  this  case,  the  figures  as  they  mingle 
together  appear  to  the  eye  as  a  cross.  If  a  bird  be  drawn  on 
one  side  of  the  card,  and  a  cage  on  the  other,  the  mingling  of 
the  two  figures,  as  the  card  revolves,  will  show  you  the  bird  in 
the  cage. 

There  are  many  other  points  in  regard  to  the  phenomena  of 
vision,  which  it  would  be  interesting  to  notice.  But  it  would 
make  this  chapter  too  long. 

472.  The  means  by  which  so  delicate  an  organ  as  the  eye 
is  protected  from  injury,  are  worthy  of  notice.  Observe  first 
its  situation.  Parapets  of  bone  surround  it,  and  receive  the 
force  of  most  of  the  blows  that  come  upon  that  part  of  the 
face.  Above  is  the  strong  arch  of  bone,  forming  the  lower 
part  of  the  forehead.  Then  there  are  the  cheek  bones,  and  the 
bones  of  the  nose.  Thus,  walled  in,  in  all  directions  by  these 
prominences,  the  eye  is  seldom  hurt,  except  by  a  direct  thrust. 
And  besides  being  thus  protected  by  surrounding  bones,  it  re- 
poses upon  a  soft  cushion  of  fat,  which  yields,  if  the  eye  be 
pushed  backward  by  violence.  Indeed  it  is  thus  pushed  back- 
ward effectually  by  the  muscle  that  closes  the  eyelids,  whenever 
an  impending  blow  is  seen,  and  it  is  thus  sunk  farther  back  in 
its  cushioned  recess,  amid  the  projecting  parapets,  and  of  course 
receives  less  of  the  force  of  the  blow  than  it  otherwise  would. 
This  muscle,  also,  by  its  instantaneous  action,  prevents  many 


316 


HUMAN  PHYSIOLOGY. 


Eye  defended  by  the  eyebrows,  eyelashes,  and  lids.    The  tears  wash  it. 


light  articles  from  flying  into  the  eye.  Such  articles  are  also 
often  prevented  from  entering  the  eye,  by  being  intercepted  by 
the  eyelashes.  The  eyebrow,  beside  being  an  ornament,  pro- 
tects the  eye  from  harm,  by  preventing  the  salt  perspiration 
from  running  down  into  the  eye,  and  irritating  it.  It  acts  as  a 
thatched  roof,  projecting  from  the  arch  over  the  eye,  and  letting 
the  perspiration  from  the  forehead  evaporate  from  it,  when  it 
is  small  in  amount,  or  drop  from  it  down  upon  the  cheek,  when 
it  is  abundant.  The  eyelashes  also  serve  to  keep  the  perspira- 
tion of  the  eyelids  from  entering  the  eye.  The  structure  of  the 
eyelids  is  such,  that  the  freest  motion  is  allowed,  while  they 
afford  by  their  firmness  considerable  protection  to  the  organ. 
They  derive  their  firmness  from  a  fibrous  cartilage,  which  makes 
the  body  of  each  lid.  You  can  readily  see  that  this  cartilage, 
making  an  even  pressure  on  the  surface  of  the  eye,  must  often 
prove  an  effectual  defense  against  direct  thrusts.  If  the  weapon 
hit  this  cartilage,  it  acts  as  a  firm  shield,  to  ward  off  the  blow 
from  the  eye  behind  it.  And  even  that  part  of  the  lid  which 
is  intended*  by  its  laxness  to  allow  free  motion  to  the  lid,  the 
skin,  is  often  an  effectual  defense.  If  an  impending  blow  be 
seen,  and  the  eye  be  instantaneously  and  forcibly  shut,  the 
wrinkled  skin  forms  a  soft  cushion  over  the  eye,  and  thus  not 
only  covers  it  up,  but  serves  materially  to  deaden  the  force  of 
the  blow. 

473.  The  tear  apparatus 
affords  the  eye  material 
protection.  The  bland  tears 
keep  the  organ  properly 
lubricated,  so  that  its  con- 
stant motions  occasion  no 
irritation.  And  if  any  thing 
gets  into  the  eye,  the  tears 
are  manufactured  abund- 
antly, for  the  purpose  of 
washing  out  the  intruding 
substance,  which  is  generally 
effected.  Fishes  have  no 
need  of  a  tear  apparatus,  as 
their  eyes  are  washed  con- 
stantly by  the  water  in 
which  they  live.  In  Fig. 
179  is  represented  the  tear- 
apparatus.  The  tears  are  TEAR  APPARATUS. 


FIG.  179. 


THE  EYE.  317 


Tear  apparatus.     Oiling  the  eyelashes. 


secreted  by  a  small  gland,  called  the  lachrymal  gland,  situated 
at  a,  in  the  orbit  under  the  arch  of  the  forehead,  and  near  the 
outer  angle  of  the  eye.  At  b  are  the  ducts  which  empty  the 
tears  in  upon  the  surface  of  the  eye  on  the  inside  of  the  upper 
lid.  By  the  constant  motions  of  the  organ  the  tears  are  diffused 
over  its  whole  surface,  and  thus  continually  wash  the  eye.  The 
arrangement  for  carrying  off  the  fluid  is  this.  It  flows  through 
a  tube,  c?,  e,  into  the  nose.  This  tube  has  at  its  beginning  in 
the  eye  two  branches,  c,  c,  which  open  on  the  edges  of  the  two 
lids  at  the  inner  corner  of  the  eye.  These  open  mouths,  that 
drink  up  the  tears  as  they  flow  to  them,  you  can  very  readily 
see.  The  drain  of  the  eye,  which  thus  conveys  the  lachryma. 
fluid  to  the  nose,  is  ordinarily  capable  of  taking  care  of  all  the 
tears  that  the  gland  makes.  But  when  an  uncommon  amount 
is  made,  as  in  weeping,  it  cannot  receive  all  the  tears,  and  they 
therefore  overflow  their  banks,  the  edges  of  the  eyelids.  And 
sometimes  there  is  a  constant  overflow  from  obstruction  of  the 
drain  by  disease.  The  continual  weeping  of  the  eye,  when  this 
obstruction  exists,  will  give  you  some  idea  of  the  amount  of  fluid 
which  the  lachrymal  glands  make. 

474.  Along  on  the  edge  of  each  eyelid  are  some  very  small 
glands  which  secrete  an  oily  substance.     This  serves  two  pur- 
poses.    It  oils  the  eyelashes.     It  also  prevents  the  tears,  when 
they  are  only  in  ordinary  quantity,  from  being  diffused  over 
the  edges  of  the  eyelids  in  the  constant  motions  of  the  eye. 
This  exceedingly  small  quantity  of  oily  substance  suffices  to 
keep  the  tears  in  the  eye  where  they  are  needed.     There  i? 
also  a  curious  provision  for  directing  the  tears 

to  the  mouths  of  the  ducts  when  the  lids  are  FIG<  18°- 

closed.  When  brought  together  their  edges 
unite  in  such  a  manner  as  to  form  with  the 
surface  of  the  eye  a  triangular  channel  for  the 
tears  to  run  in.  This  is  made  clear  by  the 
diagram  in  Fig.  180,  in  which  the  line  b  rep- 
resents the  surface  of  the  eye,  and  a  the  edges 
of  the  lids,  showing  a  section  of  the  canal  be- 
tween them. 

475.  I  had  intended  to  notice  some  of  the 
peculiarities  of  the  eyes  of  different  classes  of 

animals,  but  this  chapter  is  already  so  long  that  I  will  notice 
but  one  —  the  nictitating  membrane  in  the  eyes  of  birds. 
When  not  in  use  it  is  gathered  up  in  the  inner  corner  of  the 
eye.  When  it  is  stretched  over  the  organ  it  is  a  thin  translu- 

27* 


318 


HUMAN  PHYSIOLOGY. 


Nictitating  membrane  in  the  eyes  of  birds. 


cent  membrane.  It  is  very  elastic,  so  that 
as  soon  as  the  muscles  that  sweep  it  so 
quickly  over  the  eye  are  relaxed,  it  flies 
back  at  once  to  the  corner  where  it  is  so 
snugly  folded.  In  Fig.  1 8 1  it  is  represented 
as  half  way  over  the  front  of  the  eye.  In 
Fig.  182  are  seen  the  curiously  arranged 
muscles  that  move  it.  One  of  the  muscles, 
g,  arises  from  the  ball  of  the  eye  at  its  up- 
per part,  and  running  back  forms  by  the 
trunk  of  the  optic  nerve  a  tendon  with  a 
loop,  through  which  the  tendon  of  the  other 
muscle,  p,  works.  This  muscle  arises  from 
the  lower  part  of  the  ball  of  the  eye,  op- 
posite to  the  origin  of  the  first  muscle.  Its 
tendon,  t,  is  fastened  into  the  edge  of  the 
nictitating  membrane.  It  acts  through 
the  loop  as  a  pulley,  and  you  can  see  that 
the  muscle,  y,  assists  it  materially  in  effecting 
the  very  quick  motions  of  the  membrane. 


FIG.  181. 


FIG.  182. 


CHAPTER  XVII. 


CONNECTION  OF  THE  MIND  AND  THE  BODY. 

476.  IN  the  Chapter  on  the  Nervous  System  I  gave  you  a 
general  view  of  its  functions  and  its  arrangements.  You  saw 
that  it  is  to  the  mind  the  grand  means  of  communication  with 
the  world  of  material  and  immaterial  things  around  it.  In  the 
Chapters  on  the  Senses  and  the  Organs  of  Locomotion,  we  have 
considered  the  modes  in  which  this  communication  is  maintained, 
through  organs  subordinate  to  the  nervous  system.  And  you 
have  seen  that  through  the  senses  all  knowledge  of  external 
things  is  communicated  to  the  mind,  where  it  is  used  as  the 
material  of  thought  and  reflection  and  feeling ;  while,  on  the 
other  hand,  through  the  muscles  the  mind  produces  all  its  im- 
pressions upon  the  things  and  beings  on  which  it  acts.  You 


CONNECTION   OF   THE   MIND   AND   THE   BODY.      319 
The  brain  the  organ  of  the  mind.     Facts  which  prove  this. 

are  now  therefore  prepared  to  look  more  thoroughly  into  the 
connection  which  the  nervous  system  establishes  between  the 
mind  arid  the  body,  and  to  observe  some  of  the  higher  and  more 
intricate  phenomena  which  result  from  it.  It  is  to  views  upon 
these  points  that  I  shall  devote  this  and  the  following  chapter. 
477.  The  brain  is  the  organ  of  the  mind.  In  this  life  there 
can  be  no  mental  manifestations  except  through  the  agency  of 
this  organ.  The  rnind  and  the  brain  always  act  together  as  one 
thing.  This  is  manifest  in  regard  to  motion  and  sensation.  It 
is  equally  true  of  thought.  The  mind  can  think  and  excite 
motion  in  the  muscles  only  through  the  brain.  The  proofs  of 
this  are  various  and  abundant.  If  a  man  by  a  blow  upon  his 
head  have  a  portion  of  the  skull  driven  in  upon  the  brain,  so  as 
to  press  upon  it  considerably,  all  sensation  and  power  of  motion 
are  suspended.  His  mental  connection  with  the  world  around 
him  is  completely  cut  off.  And  not  only  so,  but  all  mental  ac- 
tion is  arrested.  The  mind,  thus  shut  in  from  the  world  around 
by  the  suspension  of  sensation,  does  riot  go  on  to  act  indepen- 
dently of  the  compressed  brain.  The  man  does  not  think ;  for 
if  thinking  did  occur  in  such  cases,  there  would  occasionally  be, 
as  after  dreaming,  some  recollection  of  what  passed  through  the 
mind,  after  the  pressure  is  taken  off  from  the  brain  by  the  tre- 
phine and  elevator  of  the  surgeon.  He  lives,  because  the  invol- 
untary muscles,  connected  by  their  nerves  with  the  top  of  the 
spinal  marrow,  (§  229,)  which  is  uninjured,  carry  on  the  breath- 
ing and  the  circulation.  But  though  he  lives,  he  is  not  now  a 
moving,  or  a  sentient,  or  a  thinking  being.  His  mind  is  as 
dormant  as  life  is  in  a  state  of  hibernation. 

478.  The  same  state  of  things  occurs  in  apoplexy,  and  in  the 
senseless  state  which  accompanies  most  convulsions.     And  it 
may  be  remarked,  that  the  degree  of  the  suspension  of  the 
mental  functions  depends  upon  the  degree  of  effect  produced 
upon  the   brain.     If,  for  example,  in  the  case  of  injury,  the 
pressure  of  the  bone  driven  in  upon  the  brain  be  not  very  great, 
the  suspension  will  be  partial ;  but  if  the  pressure  be  considera- 
ble the  suspension  will  be  complete. 

479.  The  dependence  of  the  mind  upon  the  brain  is  mani- 
fested in  a  great  variety  of  diseases.     The  delirium  of  fever  and 
of  inflammation  of  the  brain,  and  insanity  resulting  from  chronic  ' 
disease  in  this  organ,  show  this  absolute  and  inseparable  con- 
nection of  the  mind  with  the  material  organization  in  our  present 
state  of  being.     We  sometimes  see  the  mind  gradually  blotted 
out  by  the  progress  of  disease  in  the  brain,  so  that  a  man  of 


320  HUMAN   PHYSIOLOGY. 

Insanity  a  disease  of  the  organization.    Situation  of  the  brain. 

even  high  mental  powers  becomes  a  drivelling  idiot.  So,  too, 
a  bad  formation  of  the  brain,  or  early  disease  of  this  organ 
often  prevents  mental  development.  Insanity  is  always  the  re- 
sult of  disease  in  the  organization.  This  is  so  even  when  it  is 
produced  by  moral  causes  acting  directly  upon  the  mind.  The 
insanity  in  such  a  case  is  an  indirect  effect — the  organization 
affected  by  the  mind  is  thrown  into  a  diseased  state  and  reacts 
upon  the  mind,  influencing  its  manifestations.  "If  the  mind 
thus  acted  upon  were  a  spirit,  separated  from  the  body,  the 
result  would  be  merely  the  feelings,  which  the  motives  applied 
would  naturally  produce,  and  not  the  unnatural  feelings  of 
insanity.  It  is  not  strictly  proper  then  to  speak  of  a  'mind 
diseased.'  Let  me  not  be  understood  to  mean  that  mental  de- 
rangement in  every  case  is  to  be  attributed  to  disease  that  leaves 
such  palpable  traces,  that  the  dissecting  knife  would  reveal  it  if 
death  were  to  take  place.  There  are  diseased  operations  of  the 
body,  that  are  hidden  from  our  view — so  hidden,  that  they  not 
only  leave  no  traces,  but  often  develop  no  characteristic  bodily 
symptoms."*  I  shall  recur  to  this  subject  of  the  dependence 
of  the  mind  upon  the  brain  in  another  part  of  this  chapter,  and 
shall  endeavor  to  point  out  definitely  what  are  the  teachings  of 
physiology,  of  our  consciousness,  and  of  revelation  respectively 
in  regard  to  it. 

480.  Observe  for  a  moment  the  situation  and  the  immediate 
connections  of  the  brain,  the  organ  of  the  mind.  Its  situation 
in  the  human  structure  is  appropriately  a  commanding  one.  It 
is  fitly  placed  at  the  summit  of  the  structure,  inclosed  by  that 
noble  dome  which  I  described  to  you  in  the  Chapter  on  the 
Bones.  And  then  observe  that  in  its  immediate  neighborhood 
are  the  organs  of  four  of  the  senses,  sending  their  messages 
continually  to  the  mind.  Especially  you  notice  that  under  the 
jutting  arches  of  the  front  of  the  dome  are  the  ever-moving 
eyes,  looking  out  from  their  elevated  place  of  observation ;  and 
at  the  sides  of  the  base  of  the  dome  are  the  halls  of  audience, 
ever  open  and  ready  to  transmit  the  messages  that  come  to  the 
soul  through  the  vibrations  of  the  air.  And  there,  too,  in  the 
very  front  of  this  habitation  of  the  mind  is  the  face,  indicating 
by  the  delicate,  quickly  changing  play  of  its  muscles  the  thoughts 
that  are  at  work  within.  And  lastly,  there  is  the  mouth,  the 
outlet  for  the  voice,  the  chief  agent  of  the  outward  manifesta- 
tions of  the  mind.  Here  then  are  clustered  together  in  this 

*  "Physician  and  Patient,"  page  292. 


CONNECTION  OF  THE  MIND  AND  THE  BODY.      321 

Rapidity  of  communication  between  the  mind  and  the  body. 

small  space,  in  the  immediate  neighborhood  of  the  mind's  hab- 
itation, its  principal  instruments  of  communication  with  the 
world  around.  When  we  are  listening  to  eloquence,  whether 
it  be  in  the  public  assembly,  or  in  the  social  circle,  or  in  the 
more  private  intercourse  of  friendship,  and  observe,  as  the  rich 
tones  proceed  from  the  mouth,  the  elevated  and  changeful  ex- 
pressions of  the  countenance,  we  are  impressed  with  the  idea, 
that,  if  it  be  the  mind  which  constitutes  the  image  of  God  in 
man,  the  face  of  man  thus  situated  in  the  front  of  the  mind's 
habitation,  is  the  fitting  outward  emblem  of  that  image. 

481.  It  is  interesting  to  observe  how  exceedingly  rapid  are 
the  communications  of  the  mind  with  the  different  parts  of  the 
body.     Notice  what  the  process  is,  or  rather  what  the  processes 
are,  when  you  withdraw  your  hand  from  any  thing  that  hurts  it, 
as  heat  for  example.     An  impression  is  produced  upon  the  ex- 
panded nerve  in  the  part — this  impression  is  sent  along  the 
nervous  tubuli  to  the  brain — the  mind  there  receives  the  im- 
pression— the  mind  in  return  communicates  an  impression  to 
the  brain — this  impression  goes  by  another  set  of  nervous  tubuli 
to  the  muscles — they  act,  and  the  hand  is  withdrawn.     If  it 
took  as  long  to  do  all  this  as  it  has  for  me  to  describe  it,  the 
hand  would  be  very  thoroughly  burned  before  it  is  drawn  away. 
The  same  set  of  processes  is  gone  through  with,  when  in  ex- 
ecuting music,  either  with  the  voice  or  an  instrument,  a  mis- 
take is  immediately  heard  and  corrected.     And  so  of  other 
cases. 

482.  In  the  Chapter  on  the  Muscles  I  spoke  of  the  great  va- 
riety in  the  motions  of  the  body.     In  executing  these  motions 
the  individual  commonly  knows  nothing  of  the  muscles  with 
which  he  does  it.     Even  the  anatomist,  who  is  familiar  with  the 
situation  and  arrangement  of  the  muscles,  seldom  thinks  of 
them  while  he  works  them  in  the  production  of  different  mo- 
tions ;  and  if  he  does  think  of  them  it  affords  him  no  assistance 
in  their  use.     Great  skill  can  be  acquired  in  the  use  of  the 
muscles,  without  any  knowledge  in  the  individual  of  the  fact  that 
he  has  such  organs.     In  muscular  action  men  commonly  move 
a  machinery  of  which  they  know  nothing.     They  have  only  to 
will  any  particular  motion,  and  the  nerves  are  so  arranged  at 
one  end  with  the  muscular  fibres  that  will  do  it,  and  with  the 
brain   at  the  other,  that  the  message  from  the  mind  goes  to 
exactly  the  right  fibres,  and  the  result  is  produced.     For  the 
infinite  variations  of  motion  in  the  body  what  complicated  and 
intricate  arrangements  are  needed !     These  variations,  it  is  to 


322  HUMAN   PHYSIOLOGY. 


Skill  in  the  .use  of  the  muscles.     Variety  in  their  action. 

be  remembered,  do  not  result  merely  from  combinations  of 
movements,  but  are  rendered  vastly  more  extensive  from  the 
varying  degrees  of  contraction  in  the  muscles.  If  each  muscle 
always  acted  just  so  much  and  no  more,  there  would  be  even 
in  that  case  great  variety  of  motion,  from  its  combination  in 
various  ways  with  other  muscles.  But  the  variety  is  made  to 
be  endless  from  the  endless  variation  in  the  degree  of  their  con- 
traction. And  for  each  one  of  these  variations,  both  in  degree 
and  combination  of  action,  there  must  be  a  different  message 
sent  from  the  mind  along  the  nerves.  In  every  motion  the 
muscles  that  produce  it  must,  so  to  speak,  be  told  to  act,  and  not 
only  so,  but  they  must  be  told  just  how  far  to  act.  In  motions 
that  are  very  compound,  and  at  the  same  time  exceedingly  del- 
icate in  their  variation,  the  accuracy  and  variety  of  the  mes- 
sages thus  sent  from  the  brain  along  the  nerves  are  not  only 
wonderful,  but  are  beyond  our  conception.  We  realize  this 
fully,  when  with  the  views  above  expressed  in  the  mind,  we 
watch  a  skillful  balancer,  as  he  executes  his  endlessly  varied  but 
exact  movements.  So,  too,  when  we  hear  from  Ole  Bull's  one 
violin  such  a  mingling  of  sounds,  that  we  feel  that  there  must 
be  a  half  a  dozen  violins  played  upon  at  once,  how  inconceivably 
rapid  and  numerous  and  complicated  must  be  the  messages  that 
fly  from  his  brain  along  the  nerves  to  the  muscles,  and  yet  there 
is  not  a  failure  in  one  of  them — not  a  fibre  that  does  not  con- 
tract at  the  right  moment,  and  in  the  right  degree  ! 

483.  The  use  which  the  mind  makes  of  all  the  machinery  of 
the  senses  and  of  the  organs  of  locomotion  does  not  come  to  it 
at  the  outset.  It  comes  by  training,  and  in  some  cases  by  very 
long  training.  The  child  at  first  uses  its  muscles  bunglingly. 
It  does  not  see  or  hear  skillfully.  It  knows  nothing  at  the  first 
of  the  colors,  or  shapes,  or  distances  of  objects.  It  knows  nothing 
of  the  direction  or  distance  of  sounds.  It  has  all  these  things 
to  learn.  And  for  this  purpose  the  organs  of  sense  and  the 
muscles  are  put  into  exercise  at  once,  and  the  child  begins  its 
long  process  of  learning  on  the  day  of  its  birth.  Few  have  any 
conception  of  the  amount  of  knowledge  which  is  acquired  in 
the  first  of  the  child's  life.  He  is  born  not  only  with  absolutely 
no  knowledge  of  the  world  of  things  around  him,  but  he  has 
no  skill  in  the  use  of  the  instruments,  the  muscles  and  the 
senses,  by  wrhich  he  is  to  obtain  his  knowledge.  These  give 
him  at  first  no  very  definite  information ;  but  by  the  constant 
exercise  of  them,  and  by  comparisons  between  the  reports  of 
the  different  senses  he  soon  adds  rapidly  to  his  stock  of  knowl- 


CONNECTION   OF  THE   MIND   AND  THE   BODY.      323 

Learning  to  use  the  muscles.     Their  action  at  first  njtnle?s  and  awkward. 

edge,  and  becomes  skillful  in  the  use  of  his  means  of  gathering 
it.     But  let  us  see  a  little  more  particularly  how  this  is  done. 

484.  I  will  speak  first  of  the  progress  of  the  child  in  learning 
how  to  use  his  muscles.  When  he  first  puts  them  into  action 
you  see  that  he  has  no  skill  in  using  them.  The  action  is  aim- 
less and  awkward.  You  see  in  his  movements  none  of  that 
native  grace  of  which  so  much  is  said.  This  is  to  be  acquired, 
and  all  that  is  native  about  it  is  the  power  of  acquiring  it.  He 
learns  to  execute  very  many  motions  before  he  comes  to  that 
complicated  movement  of  so  many  muscles,  creeping,  and  then 
the  no  less  complicated  but  more  difficult  one  of  walking  suc- 
ceeds. How  awkwardly  he  does  this  in  his  first  attempts  to 
preserve  his  balance,  and  how  many  failures  must  he  encounter 
before  he  can  perform  this  motion  even  decently  well !  The 
same  thing  can  be  said  of  learning  to  talk  or  to  sing,  for  this  is 
but  a  training  of  the  muscles.  It  is  thus  gradually  that  all  the 
voluntary  muscles  become  educated.  It  is  true  even  of  the 
muscles  of  the  face.  At  the  first  how  expressionless  ordinarily 
is  the  face  of  a  child.  You  see  nothing  of  those  delicate  move- 
ments of  the  muscles  which  in  after  years  express  every  varying 
shade  of  thought  and  feeling.  When  he  cries  there  is  an  awk- 
ward over  action  of  the  muscles,  as  represented  in  Fig.  183. 

FIG.  183. 


He  learns  to  use  these  muscles  partly  at  least,  by  imitation. 
His  first  lesson  ordinarily  is  in  smiling,  which  he  soon  learns 
by  imitating  the  smile  of  his  mother.  But  even  this,  simple 


324  HUMAN  PHYSIOLOGY. 

Skill  in  the  use  of  the  senses  and  the  muscles.     Comes  later  in  man  than  in  animals. 

as  it  is,  he  does  awkwardly  at  first,  and  he  must  go  through  it 
long  process  before  he  can  master  all  the  capabilities  of  ex- 
pression in  these  little  muscles. 

485.  Skill  in  the  use  of  the  muscles  varies  quite  as  much  as 
any  other  acquirement  in  different  individuals.     It  is  wonderful 
in  the  juggler,  the  rope  dancer,  the  skillful  player  on  a  musical 
instrument,  and  the  accomplished  singer.     You  will  have  some 
conception  of  what  education  can  do  for  the  muscles,  if  you 
contrast  the  awkward  balancing  of  the  child  in  walking  with 
the  agile  and  delicate  balancings  of  the  rope  dancer,  or  the 
aimless  and  uncouth  movements  of  the  infant's  hands  with  the 
rapid  and  varied  execution  of  the  player  on  an  instrument,  or 
the  monotonous  and  coarse  sounds  uttered  in  a  child's  first 
attempts  at  singing  with  the  varied  melody  of  a  skillful  singer. 

486.  The  senses  are  educated  as  well  as  the  muscles.     As 
you  see  an  infant  reaching  out  his  little  hands  awkwardly  with 
his  unskilled  muscles  towards  an  object,  it  is  manifest  that  he 
knows  not  at  what  distance  the  object  is  from  him,  and  that 
he  does  not  readily  adjust  his  eyes  to  its  distance,  so  as  to  see 
it  clearly.     He  after  a  while  by  practice  acquires  the  power  of 
doing  this.     The  same  may  be  said  of  hearing.     The  little 
muscles  which  I  described  to  you  as  so  nicely  adjusting  the 
eye  for  seeing  at  different  distances,  and  the  ear  for  hearing 
various  notes  of  sound,  require  training,  just  as  the  muscles  do 
with  which  we  walk  or  talk. 

487.  It  is  a  singular  fact  that  most  other  animals  are  born 
with  so  much  more  skill  in  the  use  of  the  muscles  and  the 
senses  than  man.     While  man  is  "  in  the  nurse's  arms,"  the 
chicken,  for  example,  walks  about  as  soon  as  it  is  hatched. 
He  does  it  at  first  awkwardly,  it  is  true,  but  he  soon  learns  all 
that  is  to  be  learned  about  it.     He  is  assisted  materially,  it  is 
to  be  remarked,  by  the  fact  that  his  feet  spread  out  over  so 
large  a  space,  that  he  has  no  hard  lessons  to  learn  in  balancing 
as  the  child  has.     But  this  is  evidently  not  all  the  difference. 
If  it  were,  the  child  should  be  able  to  creep  at  the  first,  or  even 
walk  on  its  hands  and  feet,  for  in  performing  these  motions 
there  is  no  difficulty  in  supporting  the  centre  of  gravity.     The 
same  difference  exists  also  in  regard  to  the  senses,  for  the 
chicken  seems  to  understand  distances  at  once.     As  it  runs 
about  to  pick  up  its  food  it  makes  no  mistakes  on  this  score. 
But  while  man  is  thus  at  the  first  the  most  helpless  of  animals, 
in  regard  to  both  his  muscles  and  his  senses,  by  his  process  of 
learning  he  ultimately  acquires  vastly  greater  range  and  va- 


CONNECTION  OF  THE  MIND  AND  THE  BODY.      325 


The  senses  and  the  muscles  mutual  teachers.     Exemplified. 

riety  of  motion  than  other  animals.     And  the  same  thing  can 
be  said  of  his  acquirements  through  the  senses. 

488.  The  senses  and  the  muscles  are  mutual  teachers  in 
this  education  which  I  have  described.     Thus,  in  singing,  tha 
accuracy  of  the  sense  of  hearing  in  estimating  sounds  is  ac- 
quired through  the  action  of  the  muscles  of  the  voice  while 
the  ear  is  listening.     And  on  the  other  hand,  skill  in  executing 
sounds  is  acquired  by  these  muscles  under  the  tuition  of  the 
ear.     The  dependence  of  the  senses  upon  the  muscles  is  not  as 
absolute,  however,  as  that  of  the  muscles  upon  the  senses. 
The  ear  can  be  trained  in  the  accurate  appreciation  of  sounds 
without   any  corresponding   exercise  of  the   muscles  of  the 
voice,  though  the  two  processes  are  ordinarily  to  a  greater  or 
less  extent  connected,  and  are  corrective  of  each  other.     But 
even  when  the  ear  is  trained  without  any  aid  from  the  mus- 
cles of  the  voice,  the  training  is  in  some  measure  a  train- 
ing of  muscles.     For,  as  you  saw  in  the  Chapter  on  the  Ear, 
§  415,  there  are  certain  little  muscles  that  regulate  the  tension 
of  the  drum  of  the  ear,  which  undoubtedly  go  through  a  pro- 
cess of  training  when  we  are  learning  to  distinguish  accurately 
between  different  notes  of  sound.     While  the  dependence  of 
the  senses  upon  the  muscles  is  thus  a  partial  one,  the  depen- 
dence of  the  muscles  upon  the  senses  is,  on  the  other  hand, 
complete.     Although  the  muscles  have  a  sense  of  their  own, 
a  muscular  sense,  as  Bell  cahs  it,  this  is  not  adequate  to  be 
their  sole  guide  in  action,  but  it  serves  as  a  mere  auxiliary  in 
this  respect.     This  absolute  dependence  of  the  muscles  upon 
the  senses  is  very  strikingly  s'lown  in  the  fact,  that  the  deaf 
and  dumb  are  dumb  simply  because  they  are  deaf.     The  voice 
in  them  has  no  teacher.     The  muscles  which  regulate  the  ten- 
sion of  the  vocal  ligaments,  and  those  which  articulate  the 
voice  do  not  act,  because,  as  stated  in  the  Chapter  on  the  Voice, 
§  400,  they  have  no  guide  in  their  action. 

489.  Although  I  have  spoken  of  the  education  of  the  mus- 
cles and  the  senses,  this  language  is  not  strictly  correct.     For 
the  education  is  an  education  of  the  mind  that  operates  through 
these  muscles  and  senses.     It  is  the  training  of  the  mind  in 
the  use  of  these  instruments.     This  is  very  clearly  shown  in 
cases  of  idiocy.     In  these  cases  the  defect  in  talking  is  pro- 
portioned to  the  mental  deficiency.     It  arises  from  an  inca- 
pacity on  the  part  of  the  mind  in  using  its  instruments,  the 
muscles  and  the  apparatus  of  the  senses,  and  not  from  any 
defect  in  the  construction  of  these  instruments.     The  larynx 

28 


326  HUMAN  PHYSIOLOGY. 

The  involuntary  muscles  not  educated.    Why. 

and  the  articulating  organs  of  the  voice  are  perfectly  well 
formed  in  the  idiot,  as  I  have  stated  that  they  are  in  the  deaf 
mute.  While,  in  the  case  of  the  deaf  mute  they  are  not  used 
at  all  as  vocal  organs,  because  the  mind,  through  the  absence 
of  hearing,  has  no  power  of  regulating  them ;  in  the  case  of 
the  idiot  they  are  used  to  a  limited  extent,  and  in  a  very 
bungling  manner,  because  the  capability  of  regulating  them  is 
limited  by  the  deficiency  of  the  directing  intellect.  And  what 
I  have  said  of  the  muscles  of  the  voice  in  the  idiot  is  equally 
true  of  the  muscles  of  the  face.  There  is  no  defect  of  con- 
formation, nor  is  there  any  lack  of  lustre  in  the  eye,  as  is 
commonly  supposed.  The  limited  range  of  expression  and  its 
awkwardness  arise  from  an  incapability  on  the  part  of  the 
mind  of  using  the  muscles  of  expression  with  facility  and  skill. 
The  muscles  have  an  incompetent  teacher,  and  so  learn  to  do 
but  little,  and  do  that  little  bunglingly ;  or,  to  speak  more 
correctly,  the  deficient  mind  is  not  capable  of  learning  to  use 
them  properly. 

490.  The  education  of  the  muscles  does  not  extend  to  those 
which  are  involuntary.  Though  respiration,  for  example,  is  a 
very  complicated  act  of  many  muscles,  these  muscles  require 
no  education  to  do  their  part  skillfully.  We  have  no  need  to 
superintend  them,  for  their  constant  action  is  secured  by  an 
arrangement  for  nervous  influence  which  is  independent  of  the 
mind,  as  stated  in  the  Chapter  on  the  Nervous  System.  So, 
while  the  mind  sleeps,  or  when  it  is  locked  up  in  the  stupor 
of  disease,  these  muscles  continue  to  perform  their  duty,  as 
well  as  when  we  are  awake.  The  same  substantially  can  be 
said  of  the  muscles  which  perform  the  act  of  swallowing.  Al- 
though this  is  a  very  compound,  and,  mechanically  considered, 
a  very  difficult  act,  as  shown  in  the  Chapter  on  Digestion,  §  78, 
it  is  performed  as  well  in  the  first  hour  of  the  child's  life  as  it 
is  at  any  future  period.  The  muscles  that  execute  it  need  no 
training.  And  yet  it  is  only  after  long  and  diligent  training 
that  the  purely  voluntary  muscles,  as  for  example  those  of  the 
hand,  execute  movements  which  are  no  more  complicated  and 
difficult.  The  reason  for  this  difference  is  obvious.  The  move- 
ments which  are  performed  by  the  involuntary  muscles,  such 
as  breathing  and  swallowing,  are  immediately  essential  to  the 
preservation  of  life,  and  it  is  therefore  necessary  that  they 
should  be  well  executed  from  the  first.  Their  perfect  action  is 
therefore  secured  by  a  nervous  arrangement,  which  is  indepen- 
dent of  the  mind.  The  voluntary  muscles,  on  the  other  hand, 


CONNECTION   OF  THE   MIND   AND   THE   BODY.      327 


Association  of  action  in  the  muscles  without  mental  action. 

instead  of  being  devoted,  like  the  involuntary,  to  the  main- 
tenance of  life,  act  as  the  instruments  of  the  mind,  and  there- 
fore the  mind  acquires  the  power  of  using  them  skillfully  by 
dint  of  long-continued  training. 

491.  In  the  education  of  the  muscles,  it  is  to  be  observed, 
that  although  during  the  process  of  learning  the  mind  takes 
distinct  cognizance  at  first  of  every  movement,  it  after  a  while, 
as  the  education  becomes  complete,  takes  little  or  no  notice  of 
many  of  the  movements,  except  when  some  error  occurs,  or 
some  obstacle  arises.     Thus,  when  one  is  learning  to  sing  or 
play  a  tune,  the  mind  at  first  through  the  ear  takes  a  definite 
and  distinct  notice  of  every  sound,  and  makes  a  palpable  ex- 
ertion in  every  movement.     But  after  the  tune  is  learned,  this 
ceases  to  be  the  case,  and  the  movements  seem  to  be  associated 
together,  in  some  measure  independently  of  mental  action.     So 
in  learning  to  walk  the  child  notices  each  of  his  movements 
very  distinctly.     But  when  he  has  fully  learned,  but  little 
thought  seems  to  be  expended  upon  the  motions,  except  when 
some  obstacle  appears  which  interrupts  their  regular  succession. 
When  one  walks  in  a  reverie,  the  mind  is  most  of  the  time 
wholly  abstracted  from  the  associated  movements  which  make 
up  the  compound  act  of  walking.     In  learning  to  read  the 
child  makes  a  distinct  mental  effort  in  regard  to  each  letter, 
resorting  to  every  aid  which  will  help  to  make  the  effort  a 
successful  one,  even  to  the  putting  the  finger  on  each  letter  as 
he  looks  along  the  line.     But  as  he  becomes  more  and  more 
skilled,  the  association  of  action  of  which  I  have  spoken  comes 
more  and  more  into  play.     I  will  refer  you  to  a  partial  expla- 
nation of  the  facts  above  alluded  to,  given  in  §  262,  in  the 
Chapter  on  the  Nervous  System. 

492.  It  has  been  stated  in  §  325  and  §  476  that  the  mind 
receives   impressions  only  through  the  senses,   and   imparts 
them  only  through  the  muscles.     These  act  as  the  instruments 
of  the  nervous  system,  the  senses  being  the  inlets  and  the 
muscles  the  outlets  of  communication.     And  it  has  been  gen- 
erally considered  as  a  settled  point,  that  these  are  the  sole 
channels  through  which  the  interchange  of  thought  and  feeling 
is  effected  in  our  present  state  of  being.     But  it  has  been  pre- 
tended that  other  mysterious  modes  of  communication  have  in 
these  latter  days  of  progress  been  discovered.     The  phenomena 
presented  by  animal  magnetism,  as  it  is  called,  are  claimed  by 
some  to  demonstrate,  that  there  is  in  some  cases  a  peculiar 
means  of  communication,  distinct  from  those  which  are  usually 


828  HUMAN   PHYSIOLOGY. 

Animal  magnetism.     Simple  tests  expose  it. 

employed.  It  has  been  fancied  that  something  analogous  to 
magnetism  is  the  medium  of  connection  in  such  cases,  and 
hence  the  name  of  animal  magnetism.  Through  this  medium, 
it  is  asserted,  that  thoughts  and  sensations  pass  from  one  person 
to  another,  independent  for  the  most  part  at  least,  of  the  ordi- 
nary conditions  on  which  communication  depends.  The  phe- 
nomena have  been  presented  at  different  times  under  different 
phases,  and  the  theory  framed  to  account  for  them  varies 
somewhat  from  time  to  time,  according  to  the  varying  char- 
acter of  the  phenomena,  and  the  tastes  and  imaginations  of 
the  believers  in  this  so  called  science.  Amid  all  the  various 
forms  which  it  has  thus  assumed,  with  its  corresponding  di- 
versity of  names,  one  thing  has  always  been  true  of  it,  viz., 
that  whenever  any  efficient  tests  have  been  applied,  it  is  shown 
to  be  a  large  superstructure  of  falsities  built  upon  a  very  few 
facts.  And  in  view  of  the  uniform  results  of  these  tests,  we 
may  confidently  say,  that  as  yet  there  has  been  no  satisfactory 
proof,  that  there  are  any  other  channels  of  mental  communi- 
cation, than  the  ordinary  ones  furnished  by  the  senses  and  the 
muscles.  Most  minds  are  bewildered  by  the  strange,  and  some- 
times inexplicable  things,  which  appear  in  the  exhibitions 
which  they  witness,  and  are  ready  to  adopt  any  plausible  ex- 
planation which  may  be  offered.  But  some  simple  yet  search- 
ing tests  have  thus  far,  whenever  applied,  always  sufficed  to 
expose  the  delusion. 

493.  In  illustration  of  the  manner  in  which  these  tests  de- 
molish the  lofty  pretensions  of  this  so  called  science,  I  will 
give  a  single  example.  The  exhibitor  asserted  that  whatever 
was  in  his  mind,  realized  distinctly  and  vividly,  had  its  image 
in  the  mind  of  the  subject  whom  he  magnetized,  by  means  of 
the  peculiar  connection  thus  established  between  them.  Any 
decided  sensation,  therefore,  which  he  felt,  the  subject  felt  also ; 
and  if  he  fixed  his  thoughts  upon  any  thing,  the  subject  thought 
of  the  same  thing.  I  observed  that  whatever  was  said  by  the 
subject,  in  relation  to  any  sensations  or  thoughts  in  the  opera- 
tor, was  generally  in  reply  to  questions  on  the  part  of  the 
operator  himself.  And  as  these  questions  were  sometimes 
repeated  in  various  forms  before  correct  answers  could  be  ob- 
tained, I  suspected  that  the  information  requisite  for  the  answers 
was  communicated  to  the  subject  in  this  way.  I,  therefore, 
proposed  to  the  exhibitor  to  try  some  experiments  without 
questions,  as  these,  according  to  his  theory,  were  clearly  not 
necessary ;  for,  if  there  were  such  a  channel  of  communication 


CONNECTION   OF  THE   MIND   AND  THE   BODY.      329 

Mental  phenomena  of  animal  magnetism. 

between  his  mind  and  that  of  his  subject  as  he  asserted,  the 
aid  of  the  voice  was  not  required.  The  proposition  was  man- 
ifestly so  fair  an  one  that  he  could  not  refuse  to  comply  with 
it.  But  his  experiments  performed  in  this  way  failed  altogether, 
and  the  audience,  caring  less  for  a  strict  search  for  truth  than 
for  the  continuance  of  their  amusement,  showed  little  relish 
for  the  interruption,  and  the  pseudo-scientific  exhibition  wen! 
on.  I  applied  other  tests  as  I  had  opportunity,  which  developed 
the  evidence  of  imposture  here  and  there  in  the  exhibition,  and 
though  many  sober  and  intelligent  citizens  were  deluded  with 
the  belief  that  they  had  enjoyed  a  rational  and  truly  scientific 
amusement,  I  had  no  doubt  that  the  whole  was  a  piece  of 
jugglery.  There  was  one  feature  in  the  exhibition,  which  of 
itself  was  enough  to  condemn  it  as  a  ridiculous  imposture.  The 
operator  claimed  to  have  a  sort  of  absolute  control  over  the 
subject,  so  that  at  will  he  could  hold  him  in  a  connection  with 
himself  so  insulated  that  no  impressions  could  be  imparted  to 
him  by  any  other  person,  and  yet  could  dissolve  this  connection 
and  put  him  into  connection  with  some  one  else,  with  as  much 
facility  as  a  locomotive  can  be  switched  off  from  one  track  on  to 
another.  And  ridiculous  as  this  shifting  of  mental  connections 
is,  this  was  quite  as  successful  with  the  audience  as  any  part 
of  the  exhibition. 

494.  Some  of  the  phenomena  presented  in  the  exhibitions  of 
animal  magnetism  afford  interesting  illustrations  of  the  influ- 
ence exerted  upon  the  body  through  the  mind.     The  mental 
influence,  exerted  by  the  operator  upon  his  subject,  often  causes 
a  condition  of  the  nervous  system,  which  is  analogous  to  som- 
nambulism, or  to  some  of  the  forms  of  hysteria.     The  manip- 
ulations practiced,  the  looking  the  subject  intently  in  the  eye, 
the  holding  of  a  piece  of  metal  in  the  hand  with  the  eye  fixed 
upon  it,  and  other  expedients,  help  to  produce  the  impression 
in  the  mind  of  the  subject,  that  a  mysterious  and  resistless  in- 
fluence is  coming  from  the  operator  upon  him,  and  is  stealing 
over  his  system.     It  is  not  strango  that  this  should  occasion 
such  physical  results  as  we  often  see,  when  the  mind  and  the 
nerves  are  very  susceptible.     This  is  the  simple  explanation  of 
all  that  is  positive  in  what  such  exhibitions  present  to  us.    There 
is  no  such  thing  as  a  magnetic  influence,  and  animal  magnetism 
is  a  misnomer. 

495.  The  state  of  nervous  system  often  produced  is  not  in- 
consistent with  imposture  any  more  than  hysteria  is.     As  in  the 
nervous  states  exhibited  by  this  disease  there  is  often  a  strange 

28* 


330  HUMAN   PHYSIOLOGY. 


Alliance  to  hysteria.     Suggestive  influences. 


perversion  of  the  moral  mingled  with  that  of  the  physical,  so 
there  is  also  in  the  state  produced  by  the  mental  influence  of 
the  magnetizer.  Accordingly  his  most  available  subjects  are 
women  found  here  and  there  in  every  community,  who,  through 
this  mingled  moral  and  physical  perversion,  have  acquired  a 
permanently  morbid  state  of  mind,  that  makes  them  like  to  be 
thus  petted,  and  to  be  the  wonder  of  a  gaping  multitude.  There 
is  often  in  the  exhibitions  of  animal  magnetism  self-imposition 
at  the  same  time  that  there  is  imposition  upon  others.  In  the 
case  of  travelling  exhibitors  there  has  always  been  collusion 
enough  to  stamp  the  character  of  jugglery  upon  the  exhibition. 
And  in  other  cases,  where  both  the  operator  and  the  subject 
are  honest,  there  is  delusion  in  both,  and  they  impose  not  only 
upon  themselves,  but  upon  each  other,  as  well  as  upon  those 
that  witness  the  performance. 

496.  One  of  the  peculiarities  of  the  state  of  somnambulism 
which  is  induced  by  the  magnetizer,  is  the  ready  obedience  of 
the  mind  of  the  subject  to  suggestive  influences.     It  is  alive  to 
any  suggestions  which  come  from  the  mind  to  which  it  supposes 
itself  bound  by  a  magnetic  spell,  and  is  often  in  fact  shut  up  to 
influences  from  that  source  alone,  so  as  to  be  insensible  to  in- 
fluences from  any  other  quarter.     The  somnambule  is  possessed 
with  one  idea,  and  that  an  all-absorbing  one,  because  invested 
with  such  mystery.     His  insensibility  to  all  that  is  not  in  ac- 
cordance with  this  idea  is  to  be  accounted  for  in  the  same  way 
that  we  account  for  the  fact,  that  a  wound  received  in  battle 
is  often  unfelt  till  the  excitement  of  the  battle  is  over,  and  other 
similar  facts,  as  alluded  to  in  §  226.     This  state  is  often  quite 
successfully  imitated  by  impostors ;  and  sometimes  there  is  a 
mixture  of  a  partial  real  somnambulism  with  imposture,  similar 
to  that  which  occurs  in  the  case  of  the  hysterical  condition. 
Of  course  when  this  mental  connection  is  so  easily  shifted  from 
the  operator  to  bystanders  as  was  described  in  §  493,  there  must 
be  sheer  imposture.    Whether  there  be  full  somnambulism  alone, 
or  this  in  a  partial  degree  and  mingled  with  deception,  the  in- 
fluence of  the  principle  of  suggestion  is  very  apparent.     Nothing 
can  be  done   without  questions.      Leading  questions  suggest 
ideas  to  the  mind  of  the  subject,  and  an  audience  led  on  by 
love  of  the  marvellous  and  the  exciting,  are  readily  satisfied  by 
the  coincidences  that  occur  in  the  exhibition,  while  the  failures 
are  disregarded  and  forgotten. 

497.  In  the  state  of  somnambulism  induced  artificially  by 
the  so-called  magnetizer,  as  well  as  in  that  which  occurs  from 


CONNECTION   OF  THE   MIND   AND   THE   BODY.      331 
Clairvoyance  a  false  pretension.    Little  that  is  true  in  so  called  animal  magnetism. 

other  causes,  there  is  often  an  exaltation  of  the  powers  of  the 
senses.  Thus,  sometimes  a  somnambule  can  read  through  en- 
velopes of  even  many  thicknesses,  from  an  exaltation  of  tha 
sense  of  vision.*  But  all  pretensions  to  reading  through  bodies 
that  have  no  pores  or  interstices,  as  metallic  substances,  or  to 
reading  from  other  parts  of  the  body,  as  the  pit  of  the  stomach, 
or  the  back  of  the  head,  are  impostures.  So  too  are  all  the 
pretensions  to  seeing  what  is  going  on  in  other  places,  or  inside 
of  the  body.  This  clairvoyance,  as  it  is  called,  has  precisely 
the  same  claim  upon  our  confidence  that  fortune  telling  has, 
and  no  more.  Real  searching  tests  have  always  sufficed  to  ex- 
pose its  imposture. 

498.  I  have  introduced  the  above  views  of  what  is  generally 
called  animal  magnetism,  in  order  that  you  may  be  prepared  to 
apply  the  proper  tests,  whenever  such  popular  delusions  claim 
your  confidence.     I  have  introduced  them,  also,  because,  what- 
ever real  phenomena  do  appear  in  the  exhibitions  presented  to 
us  under  this  name,  afford  some  interesting  illustrations  of  the 
influence  of  the  mind  upon  the  body.     They  add  another  chap- 
ter to  our  view  of  the  mysterious  connection  of  the  physical  with 
the  spiritual,  secured  by  means  of  that  wonderful  apparatus,  the 
nervous  system.     It  is  from  this  consideration  merely  that  they 
claim  the  attention  of  the  physiologist.     The  so-called  animal 
magnetism,  when  thoroughly  sifted  is  dissipated,  and  there  are 
left  as  a  residuum  only  a  few  phenomena,  which  offer  nothing 
particularly  new,  but  are  chiefly  interesting  from  their  analogy 
to  phenomena  with  which  we  were  already  familiar.     And  its 
boast  of  the  discovery  of  a  new  medium  of  mental  communica- 
tion is,  as  you  have  seen,  entirely  groundless. 

499.  In  the  Chapter  on  the  Nervous  System  I  spoke  of  the 
different  offices  of  the  different  central  organs  of  this  system. 
The  brain,  as  you  have  seen,  is  more  especially  connected  with 
the  mind,  and  is  the  great  instrument  through  which  mental 


*  Many  of  the  statements,  however,  of  such  cases,  could   have  been  found  to  be 

lse  if  the  proper  tests  had  been  applied.    The  failure  in  testing,  so  common  in  these 

cases,  I  will  exemplify  by  a  single  case,  which  made  some  noise  in  its  time.    It  is  a 


false  if  the  proper  tests  had  been  applied.  The  failure  in  testing,  so  common  in  these 
cases,  I  will  exemplify  by  a  single  case,  which  made  some  noise  in  its  time.  It  is  a 
case  reported  by  Col.  Stone  in  his  famous  pamphlet.  He  gave  the  clairvoyant  a 


sealed  packet  with  a  very  odd  sentence  in  it,  which  she  read,  as  the  Colonel  sup- 
posed, wilhout  opening  it.  But  how  did  he  know  that  she  did  not  open  the  packet? 
Simply  because  she  returned  it  to  him  a  day  or  two  after  apparently  in  the  same 
state  as  lie  gave  it  to  her,  accompanied  with  a  copy  of  the  sentence  contained  in 
it.  This  he  considered  good  proof,  but  it  is  defective  in  its  most  essential  point. 
If  she  could  read  the  packet  without  opening  it,  why  did  she  not  do  it  in  his  pres- 
ence ?-  There  is  not  a  particle  of  evidence  that  any  one  saw  her  do  it.  The  true 
test  was  an  easy  one.  but  it  was  not  applied.  There  is  such  a  thing  as  skill  in  open- 
ing seals  and  replacing  them  so  as  to  avoid  detection,  and  until  we  have  proof  that 
this  was  not  done  we  are  not  called  upon  to  believe  that  the  clairvoyant  read  through 
the  envelopes. 


HUMAN   PHYSIOLOGY. 
Offices  of  the  cerebrum  and  cerebellum. 

manifestations  are  made.  But  it  is  only  a  certain  part  of  the 
brain,  the  cerebrum,  a,  Fig.  72,  that  has  this  special  connection 
with  the  mind.  The  cerebellum,  6,  Fig.  72,  it  is  supposed,  is 
especially  devoted  to  the  motions  of  the  body,  for  it  is  found  in 
animals  that  it  is  developed  in  proportion  to  the  range  and  va 
riety  of  motion.  From  extended  observations  on  this  point  in 
comparative  anatomy  there  seems  to  be  good  reason  to  conclude, 
that  the  cerebellum  is  the  great  central  apparatus  for  combining 
the  various  compound  motions  of  the  body.  It  is  uniformly 
found  to  be  larger  in  those  animals  that  have  great  complica- 
tion in  their  muscular  movements,  than  in  those  in  which  these 
movements  are  of  a  simple  character.  Thus,  in  animals  whose 
most  complicated  motion  is  walking,  as  the  hoofed  quadrupeds, 
the  cerebellum  is  much  smaller,  than  in  those  animals  that  climb 
and  that  take  hold  of  things  with  their  paws.  In  man  it  is 
much  larger  than  in  any  other  animal,  for  he  walks  erect,  and 
thus  brings  into  action  a  very  large  number  of  muscles  in  this 
delicate  balancing  movement  (for  such  it  is),  and  then,  in  the 
individual  parts  of  the  body,  especially  the  hand,  he  executes  a 
great  range  of  very  complicated  movements.  It  is  more  devel- 
oped in  monkeys  and  apes  than  in  any  other  of  the  inferior 
animals,  because,  with  their  capability  of  extensive  variety  of 
posture,  and  their  power  of  seizing  objects  with  their  extremi- 
ties, they  obviously  come  nearer  to  man  than  any  other  animal 
in  the  varied  combination  of  their  muscular  action. 

500.  The  conclusions,  thus  arrived  at  by  comparative  obser- 
vations in  animals  have  been  confirmed  by  experiments.     It  has 
been  found  by  physiologists,  that  if  the  cerebellum  be  removed 
in  an  animal,  with  as  little  disturbance  as  possible  to  other  parts, 
although  the  sensibilities  remain,  and  motions  are  performed, 
the  power  of  combining  muscular  actions  in  definite  compound 
movements,  such  as  flying,  walking,  <fec.,  is  lost. 

501.  These  conclusions  have  also  been  to  some  extent  con- 
firmed by  observation  of  the  phenomena  of  disease.     The  testi- 
mony from  this  source,  however,  has  not  as  yet  been  very  decided 
for  two  reasons.     First,  because  disease  in  the  brain  is  not  apt 
to  be  confined  to  one  portion  of  the  organ.     And  secondly  and 
chiefly,  because  we  have  not  had  a  sufficient  number  of  observa- 
tions of  cases  on  this  point.     It  has  been  observed,  however,  in 
some  interesting  cases  of  chronic  disease  in  the  cerebellum,  that 
deficiency  in  the  performance  of  the  compound  movements  of 
the  body  was  a  prominent  symptom.     An  unsteadiness  of  gait 
was  remarked  in  these  cases.     The  negative  testimony  which 


N   OF   THE   MIND   AND  THE   BODY.      333 


Gray  part  of  the  cerebrum  proportioned  to  the  intelligence. 

disease  gives  us  in  regard  to  the  office  of  the  cerebellum  is  very 
conclusive.  The  mental  phenomena  of  disease,  when  it  is  fast- 
ened upon  this  particular  portion  of  the  brain,  show  that  this  is 
not  that  part  of  the  organ  where  the  thinking  is  done. 

502.  It  is  chiefly,  as  you  see,  by  observing  the  different  de- 
velopments of  the  nervous  system  in  various  animals,  in  con- 
nection with  the  different  functions  performed  by  this  system, 
that  we  can  discover  the  uses  of  its  different  parts.     In  pursuing 
observations  of  the  animal  kingdom  in  this  way,  we  find  a  more 
and  more  complicated  nervous  apparatus,  as  we  proceed  from 
the  lower  animals  up  to  man.     We  find  part  after  part  added, 
and  with  every  addition  of  a  part  we  find  new  functions.     And 
as  we  study  any  particular  part  in  relation  to  the  functions 
which  appear  as  connected  with  it,  we  see  that  these  functions 
are  prominent  in  proportion  to  the  amount  of  the  development 
of  the  part.     Thus,  as  before  stated,  we  find  the  size  of  the 
cerebellum  is  in  proportion  to  the  variety  and  complication  of 
motion  in  the  animal,  while  that  of  the  cerebrum  is  in  propor 
tion  to  the  amount  of  intelligence.     And  in  relation  to  the 
cerebrum  itself  we  find  that  the  amount  of  intelligence  depends 
on  the  amount  of  its  gray  portion,  the  vesicular  substance.     In 
man,  therefore,  this  part  of  the  cerebrum  is  very  much  greater 
than  it  is  in  any  other  animal.     It  is  the  difference  in  the  amount 
of  the  gray  substance  which  constitutes  the  grand  distinction 
between  the  brain  of  man,  and  that  of  any  of  the  higher  orders 
of  animals,  for  in  all  other  respects  his  brain  differs  very  little 
from  theirs. 

503.  In  looking  at  representations  of  the  brain,  as  in  Fig.  74, 
it  would  seem  at  first  view  that  the  gray  substance,  the  working 
part  of  the  cerebrum,  is  much  less  in  amount  than  the  white 
portion,  which  serves  only  for  transmission.     But  this  is  not  so. 
The  eye  is  deceived,  because  the  white  substance  is  all  together 
in  one  central  mass,  while  the  gray  substance  is  spread  out  in 
an  external  layer.     This  is  very  plainly  illustrated  by  Fig.  184. 
Here  the  area,  a,  contained  in  the  inner  circle,  strikes  the  eye  as 
being  larger  than  the  area,  6,  included  between  the  two  circles, 
and  yet  these  areas  are  precisely  equal. 

504.  Observe  for  a  moment  in  this  connection  the  concurrent 
evidence,  by  which  we  determine  what  the  function  of  the  gray 
substance  of  the  brain  is.     It  comes  from  two  sources.     The 
first  is  that  which  is  furnished  to  us  by  the  structure  of  the  cere- 
brum.    As  stated  in  §  206  and  §  232,  the  gray  portion  is 
made  up  of  cells,  while  the  white  portion  is  composed  of  tubuli. 


334 


HUMAN  PHYSIOLOGY. 


Quantity  of  the  gray  substance.     Phrenology  considered. 


FIG.  184. 


These  tubuli  are  such  as  we  find  in  the  nerves,  and  in  fact  are 
continuous  with  them.  We  very  properly  infer,  therefore,  that 
as  the  nerves  serve  only  for  transmission,  the  white  part  of  the 
brain  does  the  same.  Is  has,  therefore,  nothing  to  do  with  the 
thinking,  and  yet  this  we  know  from  other  facts,  (§  477  and 
499,)  is  done  in  some  part  of  the  cerebrum.  So  we  infer 
necessarily  that  it  must  be  done  in  the  gray  substance.  And 
here,  to  confirm  the  truth  of  this  inference,  comes  in  one  other 
source  of  evidence,  viz.,  the  comparison  between  different  ani- 
mals in  regard  to  the  correspondence  between  the  amount  of 
the  gray  substance  and  the  amount  of  intelligence.  This  I  re- 
marked upon  in  §  502,  and  need  not  dwell  upon  it  farther. 

505.  This  dependence  of  the  mental  faculties  upon  the  gray 
substance,  the  outer  part  of  the  brain,  seems  to  give  some  coun- 
tenance to  the  doctrine  of  phrenology.  But  there  is  no  evidence 
from  an  examination  of  this  substance  that  it  is  arranged  at  all 
in  separate  organs,  as  instruments  or  seats  of  different  faculties. 
And  all  the  facts  which  have  been  collected  in  regard  to  the 
external  conformation,  as  indicating  the  comparative  prominence 
of  different  organs  with  their  faculties,  go  to  show,  when  properly 
examined,  that  the  mapping  out  of  the  brain  which  phrenology 
does  so  definitely  is  altogether  a  fiction.  The  question  in  re- 
gard to  this  is  wholly  a  question  of  evidence.  For  although 
we  can  see  no  division  of  the  cortical  substance  into  organs,  yet 


CONNECTION   OF   THE   MIND   AND   THE   BODY.      335 
Observations  opposed  to  phrenology. 

if  the  pretensions  of  phrenology  in  regard  to  the  results  of  the 
external  examination  of  heads  are  well  founded,  we  must  ac- 
knowledge such  divisions  to  exist,  though  even  the  microscope 
cannot  reveal  to  us  their  boundaries. 

506.  It  would  lead  me  into  too  long  a  discussion  to  examine 
fully  the  evidence  in  regard  to  these  pretensions  of  phrenology. 
Besides  stating  the  general  fact,  that  the  failures  in  describing 
mental  and  moral  character  from  external  examinations  of  the 
head  are  such,  when  the  examination  is  conducted  fairly,  as  to 
exhibit  the  falsity  of  these  pretensions,  I  will  only  allude  to  one 
or  two  particular  facts,  and  dismiss  the  subject.     In  the  phre- 
nological map  of  the  cranium  there  are  located  some  half  a 
dozen  organs  along  in  the  region  of  the  eyebrows.     Now,  you 
will  remember  that  the  frontal  sinus  extends  along  in  this  lo- 
cality.    This  sinus  varies  very  much  in  size  in  different  individ- 
uals.    It  is  obvious,  therefore,  that  an  external  examination 
can  give  us  no  accurate  idea  of  the  quantity  of  brain  in  that 
locality.     Take  another  point.     Phrenologists  have  always  in- 
sisted that  there  was  the  most  positive  evidence,  from  examina- 
tions of  the  head  in  man  and  in  animals,  that  certain  faculties 
or  propensities  have  their  organs  in  the   locality  where  the 
cerebellum  lies.     But  all  this  mass  of  vaunted  evidence  is  swept 
away  by  the  discovery  stated  in  §  499,  that  the  cerebellum  is 
chiefly  concerned  in  effecting  the  compound  motions  of  the  body. 
I  might  go  on  to  examine  in  this  way  the  rest  of  the  evidence 
adduced  in  favor  of  the  truth  of  phrenology,  and  show  that 
there  is  no  satisfactory  evidence  of  the  correct  localization  of  any 
one  of  the  organs  paraded  with  such  definiteness  on  the  cranial 
map  of  this  so  called  science.     But  it  would  occupy  too  much 
space. 

507.  The  only  fact  which  seems  to  give  any  countenance  to 
phrenology  is  that  general  fact,  which  is  matter  of  common  ob- 
servation, that  the  front  and  upper  portion  of  the  brain — that 
which  occupies  the  forehead — is  commonly  developed  in  pro- 
portion to  the  development  of  the  intellect.     This  would  seem 
to  show  that  the  intellectual  faculties  have  their  seat  in  this 
part  of  the  brain.     But  it  is  far  from  proving  this  to  be  so. 
For  it  may  be,  that  a  general  enlargement  of  the  cerebrum  is 
for  some  reason  accommodated  by  having  the  forehead  enlarged, 
in  preference  to  other  portions  of  the  cranium.     For  it  is  evident 
that  a  brain  which  is  larger  alike  in  all  its  parts  than  usual, 
can,  as  it  is  a  soft  yielding  organ,  be  equally  well  accommodated, 
whether  the  cranium  be  made  of  unusual  size  in  only  one  direo- 


336  HUMAN   PHYSIOLOGY. 


Size  of  the  front  part  of  the  brain.     Facial  angle. 


tion,  or  in  all  directions.  The  fact  that  in  the  child  the  forehead 
is  more  prominent  than  in  the  adult,  is  inconsistent  with  the 
supposition  that  the  intellect  has  its  seat  especially  in  the  front 
part  of  the  brain,  for  the  child  has  more  of  the  instinctive  and 
less  of  the  intellectual  than  the  adult.  I  may  remark  in  this 
connection,  that  the  phenomena  presented  by  injuries  and  by 
disease  in  this  part  of  the  cerebrum,  have  not,  as  thus  far  ob- 
served, seemed  to  show  that  it  is  the  peculiar  seat  of  the  intel- 
lectual faculties. 

508.  The  size  of  the  anterior  portion  of  the  brain,  above  re- 
ferred to,  may  be  estimated  by  the  measurement  of  the  facial 
angle,  so  termed,  proposed  by  Camper,  a  Dutch  naturalist. 
This  angle  is  formed  by  drawing  two  lines  as  represented  in 
Figures  185  and  186.  "  The  line,  a,  6,  is  drawn  from  the  most 

FIG.  185. 


prominent  part  of  the  forehead  to  the  front  of  the  upper  jaw. 
The  line,  c,  rf,  is  intended  to  represent  the  line  of  the  base  of  the 
brain,  and  runs  from  the  orifice  of  the  ear  along  on  the  floor  of 
the  cavity  of  the  nose.  It  is  manifest  that  the  less  prominent 
is  the  forehead,  that  is,  the  less  brain  there  is  in  the  front  part 
of  the  head,  the  more  acute  will  the  angle  be  that  is  formed  by 
these  lines.  In  Fig  186,  which  represents  the  skull  of  a  negro, 
this  angle  is  more  acute  than  in  the  skull  of  the  European,  Fig. 
185.  In  animals  this  facial  angle  is  much  more  acute  than  in 
man.  In  the  monkey  tribe  it  varies  from  65°  to  30°,  while  in 
man  its  average  is  about  75°.  The  ancient  Greeks,  wishing  to 
give  the  aspect  of  great  intellectual  superiority  to  their  statues 
of  deities  and  heroes,  made  it  in  them  as  high  as  90°. 

509.  It  is  proper  to  remark  here,  that  while  it  is  clear  that, 
as  a  general  rule,  the  amount  of  intelligence  is  to  some  extent 
proportioned  to  the  amount  of  the  cerebrum,  both  in  man  and 
in  animals,  the  rule  is  not  an  invariable  one.  Size  is  far  from 


CONNECTION   OF   THE   MIND   AND  THE   BODY.      337 

Mental  difference  between  man  and  animals.     Little  difference  in  the  brain. 

being  the  only  measure  of  power  in  this  case.  What  differ- 
ences there  may  be  in  intimate  structure,  to  compare  with  the 
mental  differences,  we  know  not.  Even  where  the  rule  stated 
above  holds  good,  the  difference  in  mere  bulk  is  far  from  being 
proportionate  to  the  mental  difference.  The  mind  of  a  Newton 
or  a  Shakspeare  is  gigantic  compared  with  any  common  mind, 
but  the  brain  in  such  cases  is  not  very  much  larger  than  ordi- 
nary brains. 

510.  In  relation  to  the  evidence  drawn  from  a  comparison 
between  different  animals,  in  regard  to  the  functions  of  the 
nervous  system,  there  is  one  significant  fact  which  must  not  pass 
unnoticed.     Though,  as  we  rise  in  the  scale  of  animal  life  in 
our  observations,  we  find  every  new  addition  of  functions  coupled 
with  some  new  additions  of  structure,  until  we  come  to  the 
higher  animals,  we  do  not  find  this  to  be  so  when  we  pass  from 
them  to  man.     The  brain,  it  is  true,  is  larger  in  man  than  it  is 
in  them,  and  has  much  more  of  the  gray  substance ;  but  there 
are  no  essential  differences  of  structure  in  his  brain,  to  corres- 
pond with  the  added  mental  qualities  which  so  decidedly  dis- 
tinguish him  from  the  brutes.     These  qualities  constitute  some- 
thing more  than  a  difference  of  degree.     It  is  a  difference  of 
kind.     And,  therefore,  it  is  a  great  and  a  significant  fact,  that 
there  is  no  corresponding  difference  of  kind  in  the  organization 
of  the  brain. 

511.  The  qualities  to  which  I  refer  I  have  alluded  to  in  the  first 
part  of  this  book  (§  40).     They  are  possessed  by  every  hu- 
man  being   to   some   extent,  however   debased   he  may  be; 
and,  on  the  other  hand,  they  are  never  possessed  by  any  of  the 
inferior  animals,  however  high  their  mental  manifestations  may 
be,  and  however  much  they  may  be  improved  by  training. 
Though  there  be  so  wide  a  distance  between  such  minds  as 
Newton,  and  Milton,  and  Shakspeare,  and  the  lowest  representa- 
tive of  our  race,  yet  in  him  are  contained  the  elements  of  the 
excellence  to  which  they  arrived.     But  no  one  dare  assert  thi» 
to  be  true  of  the  very  wisest  of  the  inferior  animals. 

512.  The  distinction  between  man  and  animals  is  a  definite 
one.     It  is  as  definite  as  it  would  be  if  it  were  based  upon  differ- 
ence of  organization.     The  barrier  is  fixed ;  and  not  a  step  over 
it  has  any  animal  advanced,  with  all  the  training  which  may 
have  been  expended  upon  him.     No  animal,  however  intimate 
has  his  intercourse  been  with  man,  has  ever  acquired  man's 
habit  of  abstract  reasoning,  or  manifested  any  real  knowledge 
of  the  difference  between  right  and  wrong.     Prof.  Guyot  does 

29 


338  HUMAN   PHYSIOLOGY. 

Intimate  connection  of  the  mind  and  the  body. 


not  speak  too  strongly  when  he  says,  "I  will  even  go  farther 
than  is  ordinarily  done,  and  I  will  say,  that  there  is  an  impassa- 
ble chasm  between  the  mineral  and  the  plant,  between  the  plant 
and  the  animal ;  an  impassable  chasm  between  the  animal  and 
man"  Surely  if  the  impassable  chasm  between  minerals  and 
vegetables,  and  that  between  vegetables  and  animals,  are  worthy 
of  note  when  we  take  a  comprehensive  view  of  the  material 
world,  so  also  is  that  which  is  much  more  manifest  as  existing 
between  animals  and  man.  When,  therefore,  the  comparative 
physiologist,  in  his  examination  of  mental  manifestations  in  con- 
nection with  physical  developments  finds,  as  he  comes  to  man, 
that  in  him  are  peculiar  and  distinctive  mental  manifestations 
with  no  corresponding  physical  developments,  he  should  deem 
it  to  be  an  important  fact  in  science,  which  should  not  be  slurred 
over,  or  passed  unnoticed,  as  is  often  the  case.  I  shall  allude 
to  certain  bearings  of  this  fact  in  another  part  of  this  chapter. 

513.  In  looking  at  the  facts  presented  in  this  chapter  and 
in  that  upon  the  Nervous  System,  you  must  have  been  contin- 
ually struck  with  the  intimacy  of  the  union  between  the  mind 
and  the  body.  On  this  subject  I  thus  remark  in  another  work. 
"  There  are  various  figures  used  to  illustrate  this  connection. 
The  most  common  one  is  that  in  which  the  mind  is  spoken  of 
as  dwelling  in  the  body  as  a  habitation.  In  a  certain  sense 
this  is  true.  This  tabernacle  of  flesh,  as  the  Bible  aptly  terms 
it,  is  in  its  present  state  a  habitation,  which  the  mind  is  to  leave 
in  a  short  time,  to  return  to  it,  however,  at  length,  rebuilt  and 
refitted  in  a  more  glorious,  an  incorruptible  form,  to  dwell  in  it 
then  forever.  But  this  illustration  of  the  mysterious  connec- 
tion of  the  mind  with  the  body  is  but  a  partial  one — it  does 
not  express  the  extent  nor  the  intimacy  of  that  connection. 
The  mind  is  not  a  mere  dweller  put  into  this  habitation.  Its 
union  with  it  is  not  thus  loose  and  easily  severed.  It  is  bound 
to  its  every  nerve  and  fibre,  so  that  the  least  touch  of  the  body 
at  any  point  affects  the  mind.  Instead  of  being  put  into  the 
body,  it  has,  being  thus  interlaced,  as  we  may  say,  fibre  with 
fibre,  grown  with  its  growth  and  strengthened  with  its  strength. 
In  the  feebleness  of  infancy  the  mind  is  just  as  feeble  as  the 
body,  and  they  both  grow  together  up  to  the  vigor  and  firmness 
of  manhood,  and  both  decline  together  in  old  age.  So  close  is 
their  union  through  all  the  stages  of  life,  and  so  equally  is  each 
affected  by  the  joys  and  sufferings  of  the  other,  that  we  might 
justly  conclude  that  at  death,  when  the  tabernacle  crumbles 
into  dust,  the  mind  falls  with  it  never  to  rise  again,  had  not  a 


CONNECTION  OF  THE  MIND  AND  THE  BODY,      339 

Sources  of  evidence  in  regard  to  the  nature  of  the  connection. 

divine  revelation  told  us  that,  indissoluble  as  this  connection 
appears  during  life.  Almighty  power  will  dissever  it,  and  release 
the  soul  from  the  thousand  ties  that  bind  it  to  its  habitation,  at 
the  very  moment  of  its  destruction.  Were  it  not  for  this  assur- 
ance of  our  immortality,  we  could  look  forward  in  the  uncertain 
future  to  nothing  but  blank,  drear  annihilation,  as  awaiting  our 
minds,  just  as  it  does  the  minds  of  the  brutes  that  perish. 

514.  In  our  carefulness  to  avoid  materialism,  we  are  too  apt 
to  look  upon  the  mind  and  the  body  as  two  separate  and  inde- 
pendent things.     At  death  they  do  indeed  become  so,  but  who 
of  us  knows  that  they  would,  were  it  not  for  the  fiat  of  the  Al- 
mighty ?     Who  knows  that  there  is  not  a  necessity  for  the 
putting  forth  of  his  power  in  each  individual  case  at  the  time 
of  death,  to  prevent  the  mind  of  man  from  dying  with  his  body, 
just  as  the  mind  of  the  brute  does  with  his?     The  very  preva- 
lent notion  that  the  mind  is  essentially  indestructible,  and  that 
it  is  put  into  the  body  as  a  separate  thing,  having  the  power 
of  itself  to  leave  the  body  whenever  it  dies,  rests  on  no  sub- 
stantial proof.     That  it  is  destined  thus  to  leave  the  body  is 
quite  another  thing."* 

515.  The  nature  of  the  connection  of  the  mind  and  the  body 
is  a  great  mystery.     Still,  there  are  many  things  which  we  can 
know  in  relation  to  it.     The  sources  of  our  knowledge  on  this 
subject  are  three,  viz.,  the  investigations  of  Physiology,  the  tes 
timony  of  Consciousness,  and  that  of  Revelation.     Each  of 
these  kinds  of  evidence  throws  light  upon  the  others.      If, 
therefore,  we  use  all  of  them,  giving  to  each  its  due  limits  and 
force,  we  shall  come  to  some  certain  and  valuable  conclusions. 
But  if  we  take  any  one  of  them  alone,  we  shall  be  liable  to  be 
led  into  gross  error. 

516.  There  is  in  some  physiologists  a  disposition  to  rely  upon 
physiology  alone,  to  the  exclusion  of  the  other  sources  of  evi- 
dence, in  the  investigation  of  this  subject.     In  doing  this  they 
are  driven  to  this  alternative.     Either  they  must  be  content 
with  a  very  limited  knowledge  of  the  subject,  or  they  must  rely 
upon  mere  presumptive  evidence  for  many  of  their  conclusions. 
And  commonly  the  latter  is  the  course  which  they  pursue. 
They  are  not  content  with  the  very  limited  conclusions  to  which 
they  are  shut  up  by  the  absolute  proof  furnished  by  physiology, 
They  boldly  reason,  therefore,  upon  what   they  deem  to  be 


'"Physician  and  Patient,"  from  the  Chapter  entitled  "  The  Mutual  Influence  oJ 
the  Mind  ami  Body  in  Disease." 


340  HUMAN  PHYSIOLOGY. 

Endowments  of  matter.     Is  intelligence  one  of  them? 

probable.     And  they  are  invariably  led  into  error.     This  I  pro- 
pose now  to  show. 

517.  In  order  to  get  definite  ideas  of  the  manner  in  which 
the  erroneous  conclusions  are  arrived  at,  let  us  view  matter  in 
its  various  states  and  connections.     Unorganized  dead  matter 
you  see  to  be  entirely  different  in  some  important  respects  from 
living  organized  matter.     The  distinction  is  a  definite  one.     It 
is  easily  recognized,  and  none  but  dreamers  in  science  have 
failed  to  see  it.     Though  Robinet  and  others  of  his  class  have 
sought  to  obliterate  it,  in  carrying  out  their  fanciful  notions, 
(§  48,)  and  though  some  have  supposed  that  there  was  a  latent 
life  in  all  unorganized  matter,  ready  to  be  called  into  action  on 
the  application  of  the  appropriate  excitants,  it  is  considered  by 
all  rational  observers  as  a  settled  point,  that  there  is  an  essential 
distinction  between  common  dead  matter  and  living  matter. 
The  latter  is  endowed  with  certain   properties  that  the  former 
has  not.     They  are  termed  vital  properties.     They  control  to  a 
certain  extent  the  mechanical  and  chemical  properties  which 
both  forms  of  matter  have  in  common.     Some  suppose  that 
what  we  call  life  is  a  single  principle ;  but  others  suppose  the 
endowment  to  be  compound,  made  up  of  different  principles  or 
properties.     But  this  question  we  need  not  discuss.     All  that 
concerns  the  view  I  am  presenting  .is  the  mere  fact  of  the  en- 
dowment. 

518.  Let  us  go  a  step  farther.     Some  living  beings  have  more 
endowments  than  others.     All   have  those  of  organic  life  in 
common  (§  32).     But  there  is  an  animal  life  also,  which  by 
means  of  the  nervous  system  is  superadded  to  the  organic. 
And,  as  we  trace  the  animal  kingdom  from  the  lowest  animal 
up  to  man,  we  find  the  endowments  connected  with  this  system 
multiplied  as  we  advance,  till  in  him  they  are  more  complicated 
and  extensive  than  in  any  other  animal.     This  is  especially  true 
of  intellectual  endowments,  those  which  are  merely  instinctive 
being  more  developed  in  many,  perhaps  we  may  say  most,  of 
the   inferior   animals.     And  in   man  we  find   special  mental 
endowments,  of  which  other  animals  present  not  the  faintest 
trace. 

519.  Now  the  question  arises,  whether  intelligence  is  like 
life,  a  mere  endowment  of  matter,  or  whether  it  is  in  some 
measure  independent  of  it.     In  other  words,  whether  it  is  a 
principle  or  set  of  principles  with  which  matter  is  endowed,  or 
an  immaterial  something  which  acts  through  matter  as  its  in- 
strument.    How  much  does  bare  physiology  teach  us  on  this 


CONNECTION"  OF  THE  MIND  AND  THE  BODY. 

Reliance  on  evidence  from  physiology  alone  leads  to  materialism. 

question  ?  It  has  often  been  claimed  that  it  can  teach  us  much, 
and  the  most  bold  conclusions  have  sometimes  been  ventured 
from  this  quarter.  But  mere  speculation  has  in  all  such  cases 
been  deemed  to  be  proof.  Physiology  does  show  us,  as  I  have 
before  said,  that  the  spiritual  is  in  this  world  always  connected 
with  the  material,  and  that  mind  never  acts  independently  of 
the  matter  with  which  it  is  connected  in  the  brain.  But  it 
gives  us  no  light  upon  the  nature  of  this  connection.  It  is 
well  for  us  to  know  how  deficient  are  its  teachings  on  this  point. 
For  all  that  it  can  teach  us,  we  know  not  but  that  the  mind 
may  be  a  mere  result  of  action  in  matter.  It  neither  tells  us 
that  it  is  so,  or  that  it  is  not.  It  leaves  us  entirely  in  the  dark 
on  this  point.  Indeed  so  far  as  it  affords  presumptive  evidence, 
it  appears  to  teach,  that  mental  phenomena  are  results  of  mat- 
ter, acting  in  consequence  of  certain  endowments  or  tendencies 
imparted  to  it,  just  as  secretion  is  in  living  substances,  or  chem- 
ical action  in  those  which  are  not  living.  Accordingly  those 
who  have  relied  upon  physiology  alone  on  this  subject,  have 
adopted  various  forms  of  materialism.  Some  have  supposed 
that  thought  is  a  mere  product  of  matter,  and  that  the  brain 
secretes  it  as  the  liver  secretes  bile.  Others  have  taught  that 
the  mind  is  "  a  bundle  of  instincts,"  each  residing  in  some  par- 
ticular part  of  the  brain  as  its  organ.  This  has  been  the  doc- 
trine of  some  prominent  phrenologists. 

520.  Let  us  look  at  living  matter  in  another  point  of  view, 
and  see  to  what  physiology  alone,  if  at  all  venturesome  in  draw- 
ing conclusions,  will  lead  us.  Let  us  look  at  the  origin  and 
growth  of  the  thinking  animal.  Take,  for  example,  an  animal 
the  formation  of  which  we  traced  in  the  Chapter  on  Cell-Life, 
§  210.  The  beginning  of  the  bird  as  it  forms  in  the  egg  is  a 
simple  cell  filled  with  a  fluid.  This  produces  other  cells,  and 
soon  the  organs  and  the  limbs  of  the  animal  are  formed.  At 
length  the  animal  bursts  the  shell,  and  comes  out  not  only  a 
living  and  sentient  being,  but  a  thinking  being.  It  has  a  mind 
which  feels  desires  and  emotions,  and  prompts  the  muscles  to 
action  to  effect  its  purposes.  Organization  here  precedes  the 
development  of  mind  so  far  as  we  can  see,  and  therefore  it  would 
seem  that  mind  is  a  result  of  organization.  Especially  does 
this  appear  to  be  so,  when  we  find  that  the  amount  of  mind  in 
different  animals  is  proportioned  to  the  amount  of  a  certain  part 
of  the  organization,  the  brain.  All  this  is  as  true  of  man  as  it 
is  of  other  animals.  And  besides,  we  see  in  man  that  as  the 
organization  becomes  perfected,  the  intelligence  is  proportiona- 

29* 


34:2  HUMAN  PHYSIOLOGY. 

Action  of  formative  vessels  like  instinct,  and  even  intelligence. 

bly  increased.  In  infancy,  when  the  organization  of  the  brain 
is  imperfect,  the  intelligence  is  small  in  amount,  and  grows  with 
the  growth,  and  strengthens  with  the  strength  of  the  brain. 
And  as  the  mind  thus  grows  with  the  body,  it  appears  to  perish 
with  the  dissolution  of  the  organization,  and  in  the  case  of  the 
inferior  animals  undoubtedly  does  so. 

521.  But  it  may  be  said,  that  the  physiologist  observes  that 
the  mind  designs,  and  devises  means  to  carry  out  its  designs,  and 
this  shows  that  there  is  an  immaterial  principle  that  moves  the 
machinery  of  the  material  organization.     This  is  a  plausible 
view  of  the  subject,  but  it  is  only  plausible.     Physiology  alone 
cannot  prove  it  to  be  a  correct  view.     For,  if  we  limit  ourselves 
to  her  teachings  alone,  it  can  be  made  to  appear  by  the  same 
line  of  argument,  that  mind  is  at  work  in  all  the  phenomena 
that  we  see  in  living  beings.     In  the  formation  of  any  part,  as 
you  saw  in  §  163,  in   the  Chapter  on  Formation  and  Repair, 
the  formative  vessels  work  after  a  fixed  plan,  and  cooperate  to- 
gether to  accomplish  the  object.     They  seem  to  act  intelligently, 
as  if  they  had  a  mind  by  which  they  designed,  and  devised 
means  for  carrying  out  their  designs.     And  the  formative  and 
other  vessels  thus  act  together,  proportioning  means  accurately 
to  ends,  not  only  under  fixed  and  regular  circumstances,  but  they 
do  so  under  varying  circumstances,  to  meet  exigencies.     Thus, 
when  an  artery  supplying  a  limb  is  tied,  §  169,  the  formative  ves- 
sels enlarge  the  arteries  in  the  neighborhood,  in  order  that  the 
blood  may  be  supplied  to  the  limb  in  suitable  quantity.     That  is, 
they  construct  after  a  larger  pattern  to  meet  the  new  want,  just 
as  if  they  were  informed  of  it  and  acted  accordingly.     Take 
another  example  afforded  by  the  formation  and  discharge  of  an 
abscess,  as  described  in  §  170.     In  this  case,  as  the  abscess 
forms,  various  operations  are  going  on,  with  different  sets  of 
vessels  cooperating  together  to  effect  a  common  purpose.     And 
when  the  abscess  has  made  its  way  to  the  surface,  and  dis- 
charged itself  at  an  outlet,  a  change  comes  over  the  operations, 
in  order  to  restore  the  part  to  its  usual  state.     The  different 
vessels  accommodate  themselves  to  this  change,  as  if  they  were 
intelligent  workmen,  acting  in  conformity  to  a  design  or  plan 
of  their  own,  upon  which  they  had  agreed.     Other  examples 
might  be  cited,  both  from  vegetable  and  animal  life,  all  showing 
design  and  cooperation  in  effecting  purposes. 

522.  In  such  phenomena  we  see  a  striking  analogy  to  those 
of  instinct,  and  even  to  those  of  intelligence  also.  It  is  this 
analogy  which  has  led  some  in  their  speculations  to  adopt  the 


CONNECTION  OF  THE   MIND   AND   THE   BODY.      343 
Conflicting  evidence  of  Physiology. 

idea  that  life  and  soul  are  the  same  thing.  Hence,  too,  many 
phenomena  in  vegetable  life  are  in  common  language  often 
called  instinctive.  Thus,  it  is  said,  that  when  a  seed  sprouts, 
the  roots  instinctively  seek  the  ground,  and  the  stalk  and  branches 
instinctively  seek  the  air  and  the  light.  This  is  even  the  case 
sometimes  when  the  seed  is  placed  at  some  little  distance  from 
the  ground.  So,  too,  if  a  plant  that  naturally  grows  in  wet 
ground  is  put  into  dry  soil,  but  in  the  neighborhood  of  a  wet 
spot,  it  shoots  forth  roots  abundantly  towards  this  spot,  rather 
than  on  the  other  side. 

523.  But  the  evidence  from  physiology  does  not  all  tend  to 
materialism.      There  is  some  negative  evidence  which   has  a 
different  bearing.     I  refer  to  the  fact  stated  in  §  510,  viz.,  that, 
while  man  differs  in  his  spiritual  nature  so  widely  and  so  spe- 
cifically from  the  inferior  animals,  his  brain  exhibits  no  corres- 
ponding specific  difference  in  structure,  but  only  a  difference  in 
amount.     The  difference  in  degrees  of  intelligence  in  the  animals 
below  man  is  marked  by  a  corresponding  difference  in  the 
amounts  of  the  gray  substance.     And  if  it  were  true  that  man, 
as  some  think,  differed  from  them  only  in  having  a  higher  de- 
gree of  intelligence,  we  should  expect  to  find   in  him  a  mere 
increase  cf  this  substance.     But  as  his  mind  differs  from  theirs 
not  merely  in  degree,  but  in  kind  also,  we  should  have  reason 
to  expect,  if  mind  were  wholly  dependent  on  organization,  that 
the  anatomist  would  find  not  only  an  increase  in  the  quantity 
of  the  gray  substance,  but  also  a  difference  in  its  structure. 

524.  But  strong  as  this  evidence  is,  it  appears  to  be  strongly 
rebutted,  perhaps  almost  overborne,  by  the  other  evidence  which 
I  have  cited  from  physiology.     And  the  physiologist  might 
perhaps  say  that,  although  as  yet  no  difference  of  structure  has 
been  found  that  corresponds  with  the  mental  difference,  future 
investigations  with  the  microscope  may  discover  some  subtle 
difference  of  structure  which  now  escapes  our  notice.     But  this 
it  must  be  allowed  is  not  at  all  probable.     On  the  whole  it  may 
be  remarked,  that  the  fact  of  which  I  have  been  speaking,  although 
significant  and  valuable  as  being  coincident  with  evidence  drawn 
from  the  other  sources,  yet  considered  simply  in  connection  with 
the  physiological  evidence,  the  evidence  from  the  other  sources 
being  wholly  shut  out,  it  is  doubtful  how  much  weight  it  ought 
to  have.     The  physiological  evidence,  taken  by  itself  is  con- 
flicting, and  looking  at  the  whole  scope  of  it,  the  preponderance 
must  be  acknowledged  to  be  towards  materialism. 

525.  It  is  quite  clear  then,  that  the  physiologist  cannot  well 


344  HUMAN   PHYSIOLOGY. 


Physiologist  needs  other  evidence.     Consciousness. 


avoid  materialism,  if,  in  examining  the  connection  between  the 
mind  and  the  body,  he  rejects  all  evidence  beside  that  which 
physiology  furnishes.  He  can  be  saved  from  this  result  only  by 
being  content  with  the  narrow  limits,  to  which  he  is  shut  up,  if 
he  confine  himself  to  absolute  proof.  As  we  have  already  seen, 
the  positive  knowledge  that  physiology  gives  us  on  this  subject 
is  exceedingly  narrow.  We  soon  come  to  the  line  that  divides 
between  the  known  and  the  supposed.  And  if  we  attempt  to 
go  beyond  that,  our  conclusions  as  to  what  is  probable  will 
quite  certainly  lead  us  to  the  result  which  I  have  pointed  out. 
The  need,  therefore,  of  the  evidence  drawn  from  the  other 
sources  that  I  have  mentioned  is  most  palpable.  The  physiol- 
ogist must  confess  himself  to  be  under  the  necessity  of  going 
out  of  his  physiology,  in  order  to  learn  all  that  can  be  learned 
upon  this  subject.  At  the  best,  there  is  much  mystery  in  rela- 
tion to  it  which  we  cannot  penetrate,  with  all  the  light  that  we 
can  bring  to  bear  upon  it.  And  the  mystery  is  deep  indeed, 
when  we  call  to  our  aid  only  the  dim  light  of  physiology.  It 
needs  some  other  light  to  deliver  us  from  the  confusion  of  ideas, 
into  which  we  are  introduced  by  the  analogy  existing  between 
the  phenomena  of  life  and  instinct  and  intelligence,  in  relation 
to  their  connection  with  the  organization  of  matter.  Let  us 
look  then  at  the  evidence  which  comes  from  the  other  two 
sources,  viz.,  our  consciousness,  and  revelation. 

526.  Every  individual  is  conscious  that,  as  he  feels  and  thinks 
and  acts,  he,  that  is  his  mind  or  spirit,  acts  upon  the  structure 
of  his  body,  and  is  acted  upon  by  it.  It  is  not  a  consciousness 
that  he  as  a  material  body  does  all  this.  He  feels  that  it  is  a 
power  within  that  does  it,  and  he  instinctively  separates  in  his 
ideas  the  power  from  the  different  parts  of  the  body,  and  from 
the  body  as  a  whole.  He  is  conscious  too  of  a  responsibility  in 
relation  to  the  thoughts  and  acts  of  the  spirit  within.  He  has 
a  knowledge  of  right  and  wrong,  and  has  self-reproach  on  doing 
wrong,  and  self-approbation  on  doing  right.  It  is  this  conscious- 
ness of  a  self-acting  immaterial  spirit  in  this  material  body,  that 
constitutes  the  basis  of  all  character,  and  of  all  the  moral  rela- 
tions of  man  to  his  fellow  man,  and  to  his  Maker.  Every  body 
acts  upon  the  testimony  of  this  consciousness  as  being  valid  and 
certain  testimony.  And,  however  the  physiologist  may  reason 
about  matter  and  mind,  as  if  the  latter  were  a  mere  product  or 
endowment  of  the  former,  yet  as  a  man,  as  a  member  of  society, 
as  a  subject  of  government  and  law,  he  cannot  avoid  acting 
upon  the  ground,  that  mind  in  a  certain  sense  controls  matter, 


CONNECTION"   OF  THE   MIND  AND  THE   BODY. 

Evidence  from  consciousness  confirmed  by  Revelation. 

and  is  responsible  for  its  acts  independently  of  the  matter  with 
which  it  is  connected. 

527.  Now  the  evidence  which  this  consciousness  affords  us 
should  suffice  to  keep  us  from  the  materialism,  into  which  phys- 
iology taken  alone  would  be  apt  to  lead  us.     It  shows  us  that, 
although  the  mind  is  developed  with  the  material  organization, 
and  can  act  only  with  it,  it  is  not  its  mere  product,  nor  one  of 
its  endowments.     It  shows  us,  on  the  other  hand,  that  it  is  in 
some  measure  independent  of  matter,  and  that  its  dependence 
upon  it  is  only  a  dependence  of  connection,  matter  being  the 
instrument  of  mind,  through  which  it  acts   on  external  things^ 
and  is  acted  upon  by  them.     The  evidence  from  this  source  is 
of  a  positive  character.     We  are  driven  by  it  to  the  alternative, 
of  believing  that  the  mind  is  an  immaterial,  self-acting  agent, 
in  some  measure  independent  of  matter,  or  of  harboring  the 
impious  and  monstrous   belief,  that  the  Creator  has  implanted 
in  the  bosom  of  man  a  lie,  and  that  he  is  living  a  horrible  farce, 
acting  in  view  of  moral  relations  and  responsibilities  that  have 
no  existence. 

528.  This  positive  testimony  of  our  consciousness  is  confirmed 
by  the  testimony  of  revelation.     This  is  not  done  by  any  formal 
array  of  proof.     The  existence  of  the  spiritual  part  of  man  as 
a  self-acting  responsible  agent  is  assumed  as  a  fact  that  needs 
no  proof.     All  the  statements,  and  teachings,  and  appeals  of  the 
Bible  recognize  it  as  a  fact  known  to  the  consciousness  of  every 
man.     The  Bible,  therefore,  may  be  considered  as  simply  affirm- 
ing that  the  testimony  of  our  consciousness  on  this  point  is 
valid  testimony.     But  the  Bible  goes  farther  than  this.     It 
gives  us  one  great  fact  of  which  neither  physiology  nor  our  con- 
sciousness could  assure  us.     I  refer  to  the  mind's  immortality. 
Our  consciousness  could,  it  is  true,  give  us  presumptive  evidence 
to  show  that  the  soul  with  its  high  powers  and  aspirations  is  to 
live  after  the  death  of  the  body.     But  it  could  furnish  us  no 
absolute  proof  of  the  fact.     And  its  presumptive  evidence  would 
be  effectually  rebutted  by  the  presumptive  evidence  from  physi- 
ology, which,  as  you  have  seen,  points  in  another  direction. 
We  are  so  familiar  with  the  mind's  immortality  as  a  known  fact, 
and  we  so  uniformly  think  of  it  in  connection  with  the  death 
of  the  body,  that  we  are  not  aware  how  absolutely  dependent 
we  are  upon  revelation  for  all  that  we  know  in  relation  to  it. 
If  there  were  no  revelation,  and  death  were  to  us  an  unknown 
event,  and  we  were  now  for  the  first  time  called  upon  to  witness 
the  death  of  a  friend,  how  little  should  we  know,  and  how  con- 


346  HUMAN   PHYSIOLOGY. 

Immortality  revealed  only  by  revelation. 

fused  would  be  our  thoughts  in  relation  to  the  great  mystery 
before  us!  "What  is  it?"  we  should  ask.  "Is  it  sleep?" 
No.  We  never  saw  any  one  sleep  thus.  What  is  it  ?  Who 
can  tell  us  ?  "  And  we  should  wonderingly  watch  to  see  some 
signs  of  awakening,  not  giving  up  all  hope  till  decay  begins  its 
ravages  on  the  loved  form  before  us.  Then,  as  we  should  from 
the  dictate  of  nature,  consign  to  the  earth  the  friend  who  was 
so  recently  among  us  a  breathing,  moving,  speaking  man,  now 
a  mere  mass  of  decaying  matter,  we  should  feel  that  we  bury 
there  not  the  body  only,  but  all  that  belonged  to  that  body 
during  life — the  whole  man.  Thought  and  feeling,  as  well  aa 
life  and  motion,  would  appear  to  us,  untaught  of  God,  to  be 
extinguished  in  the  grave.  Even  if  some  one  should  utter  all 
tremblingly  the  hope,  that  there  might  be  a  subtle  spiritual 
part  of  our  friend,  that  would  some  time  in  some  form  return 
again  to  our  society,  that  hope  would  at  once  be  crushed  by 
the  reflection  that  whatever  it  was  in  our  friend  that  thought 
and  felt,  it  came  into  existence  with  the  body,  was  infantile 
when  the  body  was,  grew  with  the  growth  of  the  body,  and 
strengthened  with  its  strength,  and  therefore  now,  so  far  as  we 
can  see,  has  perished  with  it.  Nature  utters  no  voice  to  tell  us 
otherwise.  She  emits  no  light  to  illumine  the  grave.  Dark- 
ness and  silence  rest  there,  till  the  light  of  revelation  shines 
upon  it,  and  God  proclaims  man's  immortality. 

529.  I  have  thus  spoken  of  the  three  sources  of  evidence  in 
regard  to  the  connection  of  the  mind  and  the  body,  and  have 
indicated  the  character  of  the  evidence  furnished  by  each.  I 
have  shown  particularly  that  if  the  attention  be  confined  to  that 
which  is  furnished  by  physiology,  the  mind  is  apt  to  be  led  into 
materialism.  But  the  attention  should  not  thus  be  confined. 
All  the  three  kinds  of  evidence  should  be  employed  and  should 
be  brought  to  bear  upon  each  other.  If  this  be  done,  the  dis- 
crepancies in  the  evidence  from  physiology  are  cleared  up  by 
the  evidence  afforded  by  consciousness  and  revelation,  and  we 
see  the  true  value  and  bearing  of  the  fact,  that  the  specific  men- 
tal difference  between  man  and  animals  is  not  attended  with  a 
corresponding  structural  difference.  Though  this  fact  operates 
merely  as  conflicting  evidence,  when  taken  simply  in  connection 
with  the  rest  of  the  facts  developed  by  physiology ;  when,  we 
come  on  the  other  hand,  to  take  the  whole  range  of  evidence 
from  the  three  sources  spoken  of,  it  is  exceedingly  satisfactory  as 
concurring  with  the  testimony  of  consciousness  and  revelation. 
At  the  same  time,  those  physiological  phenomena,  which  taken 


MAN  AND  THE  INFERIOR  ANIMALS.  347 

Evidence  from  consciousness  and  Revelation  positive. 

by  themselves  seem  to  show  so  strongly  that  the  mind  is  wholly 
dependent  upon  organization,  are  so  interpreted  by  the  evidence 
from  the  other  sources,  that  the  dependence  is  seen  to  be  for 
the  most  part  a  dependence  of  connection  only,  the  brain  being 
the  instrument  of  the  mind. 

530.  The  evidence  from  consciousness  and  revelation  is  of  the 
most  positive  character,  and  cannot  be  set  aside  by  evidence 
from  any  other  source.  Other  evidence  may  serve  to  interpret 
it,  but  cannot  nullify  it.  The  attempt  is  sometimes  made  to  set 
it  aside  by  urging  the  presumptive  evidence  of  physiology,  as 
if  it  were  absolute  proof.  But  most  physiologists  engage  in  no 
such  futile  and  unchristian  efforts,  but  give  due  weight  to  the 
testimony  of  consciousness  and  revelation  in  all  their  investiga- 
tions of  the  mysterious  connection  of  the  mind  and  the  body. 
The  influence  of  Carpenter,  an  English  physiologist,  whose  works 
are  more  extensively  used  by  students  than  those  of  any  other 
physiologist,  is  especially  to  be  commended  in  this  respect.  And 
although  skepticism  occasionally  utters  its  plausible  falsities,  de- 
ceiving the  superficial  and  the  speculative,  we  have  no  fears 
from  present  indications  that  the  votaries  of  physiological  science 
will,  as  a  body,  be  arrayed  in  opposition  to  Christianity. 


CHAPTER    XVIII. 

DIFFERENCES  BETWEEN  MAN  AND  THE  INFERIOR  ANIMALS. 

531.  I  HAVE  already  treated  somewhat  of  the  differences  be- 
tween man  and  the  interior  animals  in  different  parts  of  this 
book,  and  especially  in  the  preceding  chapter.     But  it  has  been 
done  only  incidentally,  and  the  subject  demands  at  our  hands  a 
more  thorough  and  systematic  investigation.     This  I  propose  to 
do  in  the  present  chapter. 

532.  Lord  Monboddo  maintained  that  man  is  only  an  im- 
provement on  the  monkey,  occurring  as  a  result  from  the  general 
tendency  to  advancement  claimed  to  exist  in  nature.     He  seemed 
to  think  that  man  bore  a  relation  to  the  monkey  somewhat  like 


348  HUMAN   PHYSIOLOGY. 


Lord  Monboddo.    Nature  of  instinct  a  mystery. 


that  which  the  frog  bears  to  the  tadpole,  as  described  in  §  167, 
and  that  as  the  tadpole  becomes  the  frog,  so  the  race  of  man 
was  produced  by  a  change  at  some  remote  period  of  the  crea- 
tion, of  the  monkey  into  a  man.  This  ridiculous  notion  of  the 
erudite  but  fanciful  Scotch  philosopher  is  really  but  another 
phase  of  the  more  recent  theory  of  gradation,  or  development, 
as  it  is  sometimes  called,  which  in  different  forms  is  now  advo- 
cated by  so  many  European  philosophers.  And,  although  few, 
comparatively,  adopt  this  theory  definitely  and  fully,  there  is 
quite  a  disposition  among  many  to  obliterate  the  distinctions  by 
which  the  Creator  has  in  so  marked  a  manner  separated  man 
from  the  inferior  animals.  It  is  well,  therefore,  that  we  should 
have  a  clear  idea  of  these  distinctions. 

533.  It  is  often  very  loosely  said  that  while  man  is  governed 
by  reason,  instinct  rules  in  the  animal.*     If  it  be  meant  by  this 
that,  as  a  general  rule,  reason  predominates  in  man,  while  in- 
stinct does  so  in  animals,  the  statement  is  a  correct  one.     But 
if  it  be  meant  that  animals  are  wholly  governed  by  instinct,  and 
that  man  is  distinguished  from  them  as  a  reasoning  animal,  it 
is  not  correct.     For  some  animals  do  reason,  that  is,  if  making 
inferences  be  considered  as  reasoning.     In  tracing  out  the  differ- 
ences between  man  and  animals  I  shall  not  attempt  to  show 
what  the  nature  of  instinct  is.     This  is  a  great  mystery,  and  all 
attempts  to  solve  it  have  utterly  failed.     I  shall  content  myself, 
therefore,  with  pointing  out  some  of  the  differences  between  in 
stinct  and  reason.     In  doing  this  it  is  not  always  easy  to  say 
just  where  the  one  begins  and  the  other  ends,  so  intimately  are 
their  phenomena  often  mingled  together. 

534.  The  actions  of  instinct  are  more  unaccountable  than 
those  of  reason.     In  the  operations  of  reason  we  see  something 
of  the  processes  by  which  results  are  reached.     But  it  is  not 
so  with  instinct.     For  example,  as  a  man  travels  over  an  unex- 
plored country,  we  can  understand  by  what  means  he  obtains  a 
knowledge  of  the  country,  in  order  to  guide  him  on  his  journey. 
The  processes  of  his  reasoning  in  regard  to  this  we  can  com- 
prehend.    But  when  an  insect  travels  with  unerring  certainty 
to  its  place  of  destination  without  any  guide  marks  that  we  can 

*  Some  explanation  may  be  well  here  in  relation  to  tbe  different  uses  made  of  the  word 
animal  in  different  connections.  Here  it  is  used  in  contra  distinction  to  man.  So  it  is 
used  in  the  expression,  man  and  animals.  But  as  man  is  in  certain  senses  an  animal, 
whenever  we  wish  to  recognize  this  fact  we  speak  of  other  animals  as  the  inferior  oni- 
mals.  And  thus  in  regard  to  animals,  we  speak  of  their  higher  and  lower  orders,  the 
higher  of  course  being  those  that  approximate  nearest  to  man. 


MAN  AND  THE   INFERIOR  ANIMALS.  349 

Instinct  governed  by  invariable  rules.    Mysterious  in  its  operations. 

see,*  or  when  a  swarm  of  bees  or  a  flock  of  birds  wing  their  flight 
to  distant  places,  or  when  bees  construct  their  honey-comb  with 
the  exactness  of  mathematics  in  obedience  to  the  best  principles 
for  such  a  structure,  we  cannot  understand  the  processes  which 
lead  to  the  result.  It  seems  to  be  produced  by  an  impulse  from 
a  cause  extraneous  to  the  animal,  guiding  it  as  if  it  were  a  mere 
machine.  The  little  intelligence  of  the  animal  seems  to  have 
only  an  incidental  connection  with  this  impulse.  It,  therefore, 
merely  controls  somewhat  the  circumstances  under  which  the 
instinct  acts. 

535.  So  little  has  the  intelligence  to  do  with  the  instinct,  and 
so  nearly  mechanical  therefore  are  the  actions  of  the  latter,  that 
they  are  governed  by  an  invariable  rule.  It  is  as  invariable 
almost  as  are  the  movements  of  a  machine.  For  this  reason 
there  are  no  improvements  or  alterations  in  the  acts  of  instinct. 
The  bird  and  the  bee,  for  instance,  have  no  change  of  fashion 
in  their  architecture  from  age  to  age.  The  honey  that  fed 
John  the  Baptist,  or  that  which  was  found  by  Samson  in  the 
carcase  of  the  lion,  was  deposited  in  the  same  hexagonal  cells 

*  I  will  introduce  here  as  an  illustration,  a  little  incident  recorded  in  my  note  book 
many  years  ago.  The  account  of  it  runs  thus :  I  was  much  entertained  to-day  in  watch- 
ing the  movements  of  a  very  small  winged  insect — about  one-third  of  the  size  of  a  com- 
mon fly.  He  was  dragging  a  dead  spider  across  the  road.  Every  now  and  then  he  would 
drop  his  load,  and  run  forward  a  little,  springing  about  here  and  there,  and  then  would 
go  back  and  take  up  his  load  again.  His  movements  in  this  way  were  so  quick  and  ap- 
parently so  irregular,  that  they  seemed  to  be  without  an  object.  But  I  observed,  that 
although  he  thus  ran  about  here  and  there,  his  course  in  its  general  bearing  was  a  very 
straight  one.  Soon  a  waggon  passed  along  directly  over  where  the  insect  was,  separating 
him  from  his  load,  and  disturbing  the  whole  surface  of  the  ground.  He,  however,  soon 
found  his  toad,  and  then  with  a  good  deal  of  apparent  reconnoitering  he  went  on  again  in  the 
same  general  course.  In  the  latter  part  of  his  journey  he  travelled  over  and  amidst  a  heap 
of  stones.  Here  he  would  occasionally  leave  the  spider  and  disappear,  and  then  return 
again  to  take  his  load.  Again  a  little  farther  on  I  would  see  him  emerge  from  his  con- 
cealed pathway,  and  so  on  to  the  end  of  his  journey.  His  place  of  destination  was  a  hole 
in  the  sand  beneath  a  flat  stone.  Now,  how  did  this  insect  in  his  journey  to  his  home, 
(which  to  him  was  a  long  one,  though  only  three  rods,)  manage  to  keep  so  straight  a 
course?  Was  it  in  the  same  way  that  men  manage  in  their  journeys,  guided  by  way- 
marks,  and  by  information  obtained  from  others  ?  Following  out  this  idea,  suppose  then 
a  man  to  be  at  the  same  distance  from  his  home  in  proportion  to  his  size  that  the  insect 
was  from  his  home.  According  to  this  supposition  he  must  be  over  three  thousand  miles 
from  home.  Suppose  the  direct  line  to  his  home  lay  across  an  uninhabited  country,  so 
that  he  can  get  no  information  from  others.  This  makes  his  case  parallel  with  the  in- 
sect's, for  we  saw  him  meet  no  other  insects  on  the  road.  Now,  if  he  knew  the  exact 
direction  in  which  his  home  lay,  he  could  not,  without  his  compass,  move  with  any  pre- 
cision towards  it.  And  if  he  had  wandered  away  from  it  without  a  compass,  as  the  in- 
sect did  from  his  home,  how  would  he  know  in  what  direction  it  lay  ?  And  yet  the  insect 
travelled  towards  his  home  as  if  he  preserved  exactly  amid  all  his  wanderings  the  points 
of  the  compass.  The  surface  over  which  he  went  was  very  irregular.  He  had  to  cross 
or  wind  around  eminences,  which  were  to  him  as  large  as  hills  and  mountains  are  to  man, 
and  yet  he  was  not  embarrassed  ;  and  when  he  went  among  the  stones  he  hod  more  and 
greater  difficulties  to  encounter  than  man  meets  with  in  passing  through  the  wildest  coun- 
tries. Again,  suppose  that  the  travelling  man  should  meet  with  some  whirlwind  or  some 
convulsion  of  nature,  which  should  separate  him  from  his  burden,  and  disarrange  in  some 
measure  the  face  of  the  country  about  him,  just,  as  the  travelling  insect  was  served  by  the 
commotion  of  the  horse's  feet  and  the  wheels  of  the  waggon.  Would  he  find  his  load  as 
easily  as  the  insect  did,  and  go  on  his  way  with  as  little  hesitation  1 


850 


HUMAN  PHYSIOLOGY. 


Contrivances  in  the  nests  of  birds. 


which  are  constructed  by  the  bees  of  the  present  day.     And 
each  bird  builds  its  nest  "precisely  in  the  same  way  that  its  an- 


FIG.  187. 


NEST  OF  THE  BAYA. 

cestral  birds  have  ever  done.  Most  birds' 
nests  are  constructed  after  the  same  general 
pattern.  But  sometimes  we  observe  strik- 
ing peculiarities  to  subserve  some  special 
purpose.  Fig.  187  represents  the  nest  of 
the  Baya,  a  little  bird  of  Hindoostan.  It 
is  in  the  shape  of  a  bottle,  and  is  made  of 
long  grass.  It  is  suspended  from  a  slen- 
der branch  of  a  tree,  so  that  monkeys, 
serpents,  &c.,  cannot  reach  it.  The  en- 
trance to  the  nest  is  made  on  the  under 
side,  so  that  these  animals  cannot  enter, 
while  the  bird  itself  can  readily  fly  in.  It 
is  divided  into  apartments,  in  one  of  which 
the  female  sits  upon  the  eggs,  while  in  the 
other  the  male  bird  "  solaces  his  companion 
with  his  song  whilst  she  is  occupied  in  ma- 
ternal cares."  In  Fig.  188  is  seen  the  nest 
of  another  little  eastern  bird,  which  with 
filaments  of  cotton  taken  from  the  cotton 
plant,  sews  leaves  together  with  its  beak 
and  feet,  so  as  to  conceal  th«  inclosed  nest 
from  its  enemies. 


FIG.  188. 


NEST 
of  th«  Tailor  Bird. 


MAN  AND   THE   INFERIOR  ANIMALS.  351 


Contrivances  in  the  honey-comb.     Mathematical  principles  exactly  applied. 

536.  While  there  is  no  change  in  the  acts  of  instinct  they 
are  marked  by  perfection.  That  is,  they  are  perfectly  adapted 
to  the  purposes  to  be  effected  and  to  the  circumstances  under 
which  they  are  performed.  The  Creator,  who  directs  the  im- 
pulse that  governs  the  animal,  in  this  case  as  well  as  in  all 
others,  accurately  fits  the  means  to  the  ends  to  be  accomplished. 
There  is  nothing  in  which  this  perfection  of  instinct  is  better 
shown  than  in  the  construction  of  the  honey-comb.  The  cells 
are  made  hexagonal,  because  in  this  way  all  the  space  is  occu- 
pied— there  is  no  waste  of  room.  If  the  cells  were  made  cir- 
cular, there  would  not  only  be  a  waste  of  room,  but  a  large 
quantity  of  material  would  be  needed  to  fill  up  the  spaces  be- 
tween the  cells.  The  difference  can  be  seen  in  the  two  Figures 
189  and  190.  Each  comb,  it  is  to  be  observed  farther,  has  two 

FIG.  189.  FIG.  190 


sets  of  cells,  the  ends  of  one  set  being  arranged  against  the  ends 

of  the  other  in  a  peculiar  manner.     These  ends  are  not  flat,  but 

each  one  has  three  plane  surfaces,  forming  with  each  other  a 

particular  angle  soon  to  be  noticed,  and  uniting  together  at  the 

centre  in  a  point.     In  the  arrangement  of  these  cells,  therefore, 

a  cell  of  one  set  does  not  lie  end  to  end  with  a  cell  of  another 

set.     Its  three  surfaces  form  a  part  of 

the  bottom  or  end  of  three  cells  of  FIG-  19L 

the  other  set.     This  is  made  clear  by 

Fig.  191,  in  which  a  cell  of  one  set  is 

represented  as  it  abuts  against  a  cell 

of  the  other  set  by  one  of  its  surfaces, 

its  other  two  surfaces  forming  a  third 

part  of  the  ends  of  two  other  cells.     Now  it  has  been  found 

that  the  angle  formed  at  the  edge  of  these  surfaces  between  the 

two  sets  of  cells  is  such  as  to  secure  the  greatest  strength  with 

the  least  amount  of  material.     It  was  at  one  time  thought  that 


...•/••;•-•- 


352  HUMAN  PHYSIOLOGY. 

Wonderful  operations  of  instinct  in  communities  among  animals. 

this  was  proved  to  be  not  exactly  true.  The  variation  from  the 
correct  angle,  made  out  by  the  calculations  of  the  mathemati- 
cians, was  indeed  a  slight  one,  but  still  it  was  variation  enough 
to  show,  if  the  calculations  were  correct,  that  the  workings  of 
instinct  were  not  perfect  in  this  case.  But  the  investigations 
of  Lord  Brougham  have  satisfactorily  shown  that  the  mathe- 
maticians were  wrong  in  their  calculations,  and  that  the  bees 
are  right. 

537.  The  perfection  of  the  operations  of  instinct  is  shown  in 
the  most  wonderful  manner  in  the  regulation  of  communities  of 
animals.     Here  we  see  cooperation  to  produce  results  effected 
through  an  irrational,  and  therefore  in  some  measure  a  blind 
instinct.     This  social  instinct  is  most  extensively  exemplified 
among  the  insect  tribes,  as  for  instance  the  bee  and  the  wasp. 
The  structures,  resulting  from  the  cooperation  of  multitudes  of 
little  laborers  guided  by  this  instinct,  are  very  interesting.     I 
shall  allude  to  but  a  single  familiar  example,  the  construction 
of  the  nests  of  wasps.     These  insects  make  their  building  ma- 
terial from  the  fibres  of  old  wood.     These  they  convert  by  mas- 
tication into  a  pulp,  which  made  into  a  thin  layer,  becomes  firm 
like  paper.     It  is  indeed  a  process  very  much  like  the  common 
process  of  paper-making  invented  by  man,  and  the  first  rude 
inventor  may  have  got  his  idea  from  the  insect.     With  this 
substance  the  wasps  build  several  ranges  of  cells,  which  are 
hexagonal,  like  the  cells  in  the  comb  of  the  bee.     These  ranges 
of  cells  are  placed  parallel  to  each  other,  at  regular  distances, 
with  little  supporting  columns  between  them,  as  seen  in  Fig. 
192, 

The  number  and  variety  of  instincts  of  the  ordinary  hive  bees 
are  very  wonderful,  but  it  would  occupy  too  much  space  to  de- 
scribe them. 

538.  The  wonderful  cooperation  of  animals  in  obedience  to 
social  instinct,  in  the  building  of  habitations  and  other  struc- 
tures is  seen  in  several  of  the  mammalia.     But  it  is  most  won- 
derful in  the  beaver,  the  following  description  of  whose  habits 
in  this  respect  I  take  from  Carpenter.     "  During  the  summer  it 
lives  solitarily  in  burrows,  which  it  excavates  for  itself  on  the 
borders  of  lakes  and  streams ;  but  as  the  cold  season  approaches 
it  quits  its  retreat  and  unites  itself  with  its  fellows,  to  construct, 
in  common  with  them,  a  winter  residence.     It  is  only  in  the 
most  solitary  places  that  their  architectural  instinct  fully  devel- 
ops itself.     Having  associated  in  troops  of  from  two  to  three 
hundred  each,  they  choose  a  lake  or  river,  which  is  deep  enough 


MAN  AND   THE   INFERIOR  ANIMALS. 


353 


Exemplified  in  the  beaver  community. 


FIG.  192. 


NEST  OF  WASPS. 

to  prevent  its  being  frozen  to  the  bottom ;  and  they  generally 
prefer  running  streams,  for  the  sake  of  the  convenience  which 
these  afford  in  the  transportation  of  the  materials  of  their  erec- 
tion. In  order  that  the  water  may  be  kept  up  to  a  uniform 
height,  they  begin  by  constructing  a  sloping  dam ;  which  they 
form  of  branches  interlaced  one  with  another,  the  intervals  be 
tween  them  being  filled  up  with  stones  and  mud,  with  which 
materials  they  give  a  coat  of  rough-cast  to  the  exterior  also 
When  the  dam  passes  across  a  running  stream,  they  make  it 
convex  towards  the  current ;  by  which  it  is  caused  to  possess 
much  greater  strength  than  if  it  were  straight.  This  dam  i? 
usually  eleven  or  twelve  feet  across  at  its  base,  and  is  enlarged 
every  year;  and  it  frequently  becomes  covered  with  vegetation 
so  as  to  form  a  kind  of  hedge. 

539.  When  the  dam  is  completed,  the  community  separate* 
30* 


354  HUMAN  PHYSIOLOGY. 

Blindness  of  instinct  exemplified. 

into  a  certain  number  of  families ;  and  the  beavers  then  employ 
themselves  in  constructing  huts,  or  in  repairing  those  of  a  pre- 
ceding year.  These  cabins  are  built  on  the  margin  of  the  water ; 
they  have  usually  an  oval  form,  and  an  internal  diameter  of  six 
or  seven  feet.  Their  walls  are  constructed,  like  the  dam,  of 
branches  of  trees ;  and  they  are  covered,  on  two  of  their  sides, 
with  a  coating  of  mud.  Each  has  two  chambers,  one  above  the 
other,  separated  by  a  floor ;  the  upper  one  serves  as  the  habita- 
tion of  the  beavers,  and  the  lower  one  as  the  magazine  for  the 
store  of  bark,  which  they  lay  up  for  their  provision.  These 
chambers  have  no  other  opening,  than  one  by  which  they  pass 
out  into  the  water.  It  has  been  said  that  the  flat  oval  tail  of 
the  beavers  serves  them  as  a  trowel,  and  is  used  by  them  in 
laying  on  the  mud  of  which  their  erections  are  partly  composed ; 
but  it  does  not  appear  that  they  use  any  other  implements  than 
their  incisor  teeth  and  fore -feet.  With  their  strong  incisors  they 
cut  down  the  branches,  and  even  the  trunks  of  trees  which  may 
be  suitable;  and  by  the  aid  of  their  mouths  and  fore-feet,  they 
drag  these  from  one  place  to  another.  When  they  establish 
themselves  on  the  bank  of  a  running  stream,  they  cut  down 
trees  above  the  point  where  they  intend  to  construct  their  dwell- 
ings, set  them  afloat,  and,  profiting  by  the  current,  direct  them 
to  the  required  spot.  It  is  also  with  their  feet  that  they  dig  up 
the  earth  they  require  for  mortar,  from  the  banks  or  from  the 
bottom  of  the  water.  These  operations  are  executed  with  ex- 
traordinary rapidity,  although  they  are  only  carried  on  during 
the  night.  When  the  neighborhood  of  man  prevents  the 
beavers  from  multiplying  to  the  degree  necessary  to  form  such 
associations,  and  from  possessing  the  tranquillity  which  they 
require  for  the  construction  of  the  works  just  described,  they 
no  longer  build  huts,  but  live  in  excavations  in  the  banks  of  the 
water." 

540.  Instinct  moves  straight  on  to  its  result,  and  it  does  so 
blindly.  It  exercises  no  intelligence  in  regard  to  the  purpose 
for  which  the  result  is  intended,  or  the  circumstances  which 
tend  to  defeat  this  purpose.  It  evidently  in  some  cases  never 
knows  any  thing  of  the  purpose  aimed  at  by  its  acts,  as,  for  ex- 
ample, when  an  animal  makes  provisions  for  a  progeny  which 
it  is  never  to  see.  "  It  is  scarcely  possible,"  says  Carpenter, 
"to  point  to  any  actions  better  fitted  to  give  an  idea  of  the  na- 
ture of  instinct,  than  those  which  are  performed  by  various 
insects,  when  they  deposit  their  eggs.  These  animals  will  never 
behold  their  progeny ;  and  cannot  acquire  any  notion  from  ex- 


MAN  AND  THE  INFERIOR  ANIMALS.  355 

Results  of  instinct  mingled  with  those  of  reason. 


perience,  therefore,  of  that  which  their  eggs  will  produce ;  never- 
theless they  have  the  remarkable  habit  of  placing,  in  the  neigh- 
borhood of  each  of  these  bodies,  a  supply  of  aliment  fitted  for 
the  nourishment  of  the  larva  that  is  to  proceed  from  it ;  and 
this  they  do,  even  when  they  are  themselves  living  on  food  of 
an  entirely  different  nature,  such  as  would  not  be  adapted  for 
the  larva.  They  cannot  be  guided  in  such  actions  by  any  thing 
like  reason;  for  the  data  on  which  alone  they  could  reason 
correctly,  are  wanting  to  them ;  so  that  they  would  be  led  to 
conclusions  altogether  erroneous  if  they  were  not  prompted 
by  an  unerring  instinct,  to  adopt  the  means  best  adapted  for 
the  attainment  of  the  required  end." 

541.  The  results  of  reason  are  often  mingled  with  those  of 
instinct  in  such  a  way  that  it  is  difficult  to  distinguish  them 
from  each  other.  But  instinct  is  of  itself  wholly  irrational. 
If  it  were  not  so,  it  would  avoid  acting  whenever  action  would 
evidently  be  useless.  But  instinct  has  not  the  eyes  of  reason 
to  see  when  this  is  the  case.  It  leads  the  animal  blindly  on ; 
so  that,  although  under  all  ordinary  circumstances  the  object 
is  accomplished  definitely  and  in  the  best  manner,  yet  there  is 
no  capability  of  making  provision  for  extraordinary  circum- 
stances. Therefore,  actions  are  occasionally  performed,  which 
do  not  at  all  answer  the  purpose  which  the  instinct  is  designed 
to  effect.  Instinct,  though  perfect  in  its  action  under  the  fixed 
uniform  circumstances  under  which  it  is  destined  to  act,  is  a 
kind  of  blunderer  when  irregular  circumstances  arise.  Instinct 
is  a  strict  routinist,  while  reason  readily  accommodates  itself 
to  endlessly  varying  circumstances.  In  illustration  of  the 
above  characteristic  of  instinct,  I  will  cite  a  few  examples. 
The  hen  will  sit  on  pieces  of  chalk  shaped  like  eggs,  as  readily 
as  she  will  on  the  eggs  themselves.  Her  instinct  is  so  blind 
as  to  be  deceived  by  this  general  resemblance.  The  flesh-fly 
often  lays  its  eggs  in  the  carrion-flower,  the  odor  of  which  is 
so  much  like  that  of  tainted  meat  as  to  deceive  the  insect. 
An  amusing  illustration  of  the  blind  disregard  of  circum- 
stances in  following  out  the  promptings  of  instinct  is  given  by 
a  gentleman,  Mr.  Broderip,  in  an  account  of  a  beaver  which 
he  caught  when  very  young.  As  soon  as  it  was  let  out  of  its 
cage,  and  materials  were  placed  in  its  way,  it  began  to  build 
after  the  fashion  followed  by  these  animals  when  they  construct 
their  dam  in  a  stream  of  water  and  build  their  habitations  in  its 
banks.  "  Even  when  it  was  only  half  grown,"  says  Mr.  B.,  "  it 
would  drag  along  a  large  sweeping-brush,  or  a  warming-pan, 


856  HUMAN  PHYSIOLOGY. 

Blindness  of  instinct  illustrated  in  the  beaver. 

grasping  the  handle  with  its  teeth,  so  that  the  load  came  over 
its  shoulder ;  and  would  endeavor  to  lay  this  with  other  ma- 
terials, in  the  mode  employed  by  the  beaver  when  in  a  state 
of  nature.  The  long  and  large  materials  were  taken  first ; 
and  two  of  the  largest  were  generally  laid  cross- wise,  with  one 
of  the  ends  of  each  touching  the  wall,  and  the  other  ends  pro- 
jecting out  into  the  room.  The  area  formed  by  the  cross- 
brushes  and  the  wall,  he  would  fill  up  with  hand-brushes,  rush- 
baskets,  books,  boots,  sticks,  cloths,  dried  turf,  or  any  thing  port- 
able. As  the  work  grew  high,  he  supported  himself  on  his  tail, 
which  propped  him  up  admirably ;  and  he  would  often,  after  lay- 
ing on  one  of  his  building  materials,  sit  up  over  against  it,  ap- 
pearing to  consider  his  work,  or  as  the  country  people  say,  'judge 
it.'  This  pause  was  sometimes  followed  by  changing  the  position 
of  the  material  judged ;  and  sometimes  it  was  left  in  its  place. 
After  he  had  piled  up  his  materials  in  one  part  of  the  room, 
(for  he  generally  chose  the  same  place,)  he  proceeded  to  wall 
up  the  space  between  the  feet  of  a  chest  of  drawers  which  stood 
at  a  little  distance  from  it,  high  enough  on  its  legs  to  make 
the  bottom  a  roof  for  him ;  using  for  this  purpose  dried  turf 
and  sticks,  which  he  laid  very  even,  and  filling  up  the  interstices 
with  bits  of  coal,  hay,  cloth,  or  any  thing  he  could  pick  up. 
This  last  place  he  seemed  to  appropriate  for  his  dwelling;  the 
former  work  seemed  to  be  intended  for  a  dam.  When  he  had 
walled  up  the  space  between  the  feet  of  the  chest  of  drawers, 
he  proceeded  to  carry  in  sticks,  cloths,  hay,  cotton,  &c.,  and  to 
make  a  nest ;  and  when  he  had  done,  he  would  sit  up  under 
the  drawers,  and  comb  himself  with  the  nails  of  his  hind  feet." 
I  simply  remark  in  relation  to  this  amusing  narration,  that  you 
can  see  at  once  that  if  the  instinct  of  this  animal  had  been  at 
all  rational,  it  would  not  have  impelled  him  to  construct  a  dam 
and  a  dwelling  in  a  common  room,  where  they  would  be  of 
no  use  to  him.  Reason  would  have  dictated  the  building  of 
a  nest  and  nothing  more. 

542.  The  care  which  animals  exercise  in  relation  to  their 
progeny  seems  to  be  governed  to  a  great  extent,  perhaps  wholly, 
by  a  blind  instinct.  All  care  is  given  up  when  care  is  no  longer 
needed,  and  with  it  what  appears  to  be  affection  is  given  up 
also.  In  animals  there  is  no  such  lasting  affection  of  the  pa- 
rent for  the  progeny  as  there  is  in  man;  for  in  them  it  is 
merely  instinctive,  and  not  rational  and  moral  in  its  character, 
and  it,  therefore,  lasts  only  so  long  as  it  is  needed  to  carry  out 
the  purposes  for  which  this  particular  instinct  is  designed. 


MAN  AND  THE  INFEKIOR  ANIMALS.  357 

Difference  between  the  intelligence  of  man  and  that  of  animals. 

Indeed,  in  some  cases  there  can  be  no  affection  in  all  the  care 
which  is  instinctively  exercised  by  the  parent,  for  it  is  put  forth 
for  progeny  which,  as  stated  in  §  540,  the  animal  is  destined 
never  to  see.  And  in  those  cases  among  animals  in  which  the 
family  state  exists,  it  is  a  mere  temporary  affair,  and  as  soon 
as  the  offspring  is  able  to  take  care  of  itself  it  is  no  more  to 
the  parent  than  any  other  animal  of  the  same  tribe  is. 

543.  But  some  animals  have  intelligence  as  well  as  instinct. 
When  'this  intelligence  is  shown  in  the  mere  power  of  imita 
tion  it  is  of  a  low  order.     The  parrot  that  learns  to  imitate 
man  in  speech  is  nothing  like  as  intelligent  as  some  animals 
that  have  no  such  power.     Some  animals  have  really  a  reason- 
ing intelligence — that  is,  they  make  rational  inferences.     Their 
reasoning  is  sometimes,  as  before  remarked,  so  mingled  with 
the  operations  of  instinct,  that  it  is  difficult  to  distinguish  them 
accurately.     In  the  case  of  the  beaver  related  in  §  541,  who 
labored  so  faithfully  in  obedience  to  a  blind  instinct,  there  was 
some  exercise  of  reason,  as,  for  example,  when  he  "judged " 
his  work.     But  it  is  difficult  to  point  out  definitely  the  line 
between  instinct  and  reason  in  such  a  case.     There  are  some 
animals,  however,  in  whom  the  workings  of  a  reasoning  intel- 
ligence are  to  be  seen  with  perfect  distinctness.     But  their 
reasoning  differs  from  that  of  man.     The  inferences  which  the 
reasoning  animal  makes  are  individual ;  while  man  goes  be- 
yond this,  and  makes  general  inferences,   and  therefore  dis- 
covers general  truths.     Newton's  dog,  Diamond,  saw  apples 
fall  to  the  ground,  as  well  as  his  master.     And  he  was  capable 
of  making  some  inferences  in  regard  to  them ;  but  they  were 
individual  inferences.      For  example,  if  an  apple-tree  were 
shaken,  and  the  dog  were  hit  by  a  falling  apple,  whenever  he 
saw  other  apples  falling  he  would  infer  that  he  might  be  hit 
again,  and  would  infer  also  that  it  was  best  for  him  to  get  out 
of  harm's  way.     This  would  be  the  extent  of  his  reasonings. 
But  his  master  inquired  into  the  cause  of  the  fall  of  the  apple, 
and  by  considering  this  and  other  similar  phenomena,  he  de- 
duced general  principles,  which  govern  the  movements  both 
of  the  atoms,  and  the  worlds  of  the  universe. 

544.  The  inferences  which  are  formed  by  animals  are  mere 
results  of  the  association  of  ideas,  and  the  process,  therefore, 
really  hardly  merits  the  appellation  of  reasoning.     Thus,  in 
the  case  of  Newton's  dog,  supposed  above,  the  idea  of  the  fall- 
ing apples  was  associated  in  his  mind  with  the  hurt  experienced 

hen  he  was  hit,  and  prompted  the  getting  out  of  harm's  way. 


w 


358  HUMAN  PHYSIOLOGY. 


Reasoning  in  animals  mere  mental  association.     Exemplified. 

When  such  associations  are  extended  and  complicated,  it  ap- 
pears at  first  thought  as  if  the  animal  acted  in  view  of  general 
truths,  arrived  at  by  the  same  process  of  reasoning  that  man 
employs.  But  it  is  a  mere  extension  of  mental  associations. 
Thus,  Newton's  dog  probably  associated  the  idea  of  being  hit 
and  hurt  with  other  falling  bodies  beside  apples.  And  so,  too, 
various  circumstances  might  come  to  be  associated  with  the 
falling  of  bodies,  and  thus  complicate  the  mental  process  which 
occurred  when  he  saw  any  object  falling  near  him. 

545.  To  show  somewhat  the  extent  to  which  this  mental 
association  operates  in  the  brute  mind,  I  will  allude  to  some 
examples.  A  wren  built  its  nest  in  a  slate  quarry,  where  it 
was  liable  to  great  disturbance  from  the  blastings.  It  soon, 
however,  learned  to  quit  its  nest,  and  fly  off  to  a  little  distance, 
whenever  the  bell  rang  to  warn  the  workmen  previous  to  a 
blast.  As  this  was  noticed,  the  bell  was  sometimes  rung  when 
there  was  to  be  no  blast,  for  the  sake  of  the  amusement  in 
seeing  the  poor  bird  fly  away  when  there  was  no  need  of  alarm. 
At  length,  however,  it  ceased  to  be  deceived  in  this  way,  and 
when  it  heard  the  bell  ring  it  looked  out  to  see  if  the  workmen 
started,  and  if  they  did  then  it  would  leave  its  nest.  In  this 
case  the  bird  merely  learned  to  connect  in  its  mental  associa- 
tions two  circumstances  with  the  blasting,  instead  of  the  one 
from  which  it  at  first  took  the  warning.  The  operation  of 
this  mental  association  is  shown  in  a  little  different  manner  in 
the  following  case.  Some  horses  in  a  field  were  supplied  with 
water  in  a  trough  which  was  occasionally  filled  from  a  pump. 
As  the  supply  was  not  always  sufficient,  one  of  the  horses,  more 
sagacious  than  the  rest,  whenever  he,  on  going  to  drink,  found 
the  trough  empty,  pumped  the  water  into  it  by  taking  hold  of 
the  pump-handle  with  his  teeth,  and  moving  his  head  up  and 
down.  The  other  horses  seeing  this,  would,  whenever  they 
came  to  the  trough  and  found  it  empty,  tease  the  one  that 
knew  how  to  pump,  by  biting  and  kicking  him,  till  he  would 
fill  the  trough  for  them.  In  this  case  the  horse  that  did  the 
pumping  associated  in  his  mind  the  motion  of  the  pump-handle, 
as  he  had  seen  it  done  by  his  master,  with  the  supply  of  water. 
And  while  they  associated  this  supply  with  his  pumping,  he 
knew  what  their  teasing  him  meant,  because  he  associated  it 
with  their  motions  about  the  trough,  indicating  so  plainly  that 
what  they  wanted  was  water.  But  I  will  give  a  still  stronger 
case.  A  dog  belonging  to  a  Frenchman  was  observed  to  go 
every  Saturday,  precisely  at  two  o'clock,  from  his  residence  at 


MAN  AND  THE   INFERIOR  ANIMALS.  359 

Relation  between  cause  and  effect  learned  from  association. 

Locoyarne  to  Hennebon,  a  distance  of  about  three  quarters  of 
a  league.  It  was  found  that  he  went  to  a  butcher's,  and  for 
the  purpose  of  getting  a  feast  of  tripe  which  he  could  always 
have  at  that  hour  on  Saturday,  their  day  of  killing.  It  is  also 
related  of  this  dog,  that  at  family  prayers  he  was  always  very 
quiet,  till  the  last  paternoster  was  commenced,  and  then  he 
would  uniformly  get  up  and  take  his  station  near  the  door,  in 
order  to  make  his  exit  immediately  on  its  being  opened.  The 
narrator  of  these  facts  thinks  that  the  first  fact  shows,  that  the 
dog  could  measure  time  and  count  the  days  of  the  week.  But 
this  cannot  be  so.  The  dog  undoubtedly  associated  in  his 
mind  the  time  at  which  he  could  get  the  tripe,  with  something 
that  occurred  on  Saturday  at  that  hour  at  his  master's  house, 
just  as  he  associated  the  concluding  of  family  prayers  with 
something  that  occurred  as  the  last  paternoster  was  read,  per- 
haps with  some  peculiarity  in  the  manner  of  his  master  when 
he  came  to  that  part  of  the  service. 

546.  Animals  learn  the  relation  between  cause  and  effect  by 
this  mental  association,   and  act  upon  the  experience   thus 
gained.     This  is  manifest  in  the  examples  I  have  cited.     And 
it  may  be  observed  in  many  acts  that  we  witness  occasionally 
in  the  higher  animals.     Thus,  for  example,  as  my  horse  was 
cropping  some  grass,  he  took  hold  of  some  that  was  so  stout, 
and  yet  so  loosely  set  in  the  ground,  that  he  pulled  it  up  by 
the  roots,  and,  as  the  dirt  which  was  on  it  troubled  him,  he 
very  deliberately  knocked  it  across  the  bar  of  a  fence  till  he  got 
all  the  dirt  out,  and  then  went  on  to  eat  it.     Here  was  a 
knowledge  of  cause  and  effect  which  was  derived  from  previous 
experience  through  mental  association.     You  see  the  same 
thing  when  you  see  a  cat  jump  up  and  open  the  latch  of  a 
door,  or  a  horse  unbolt  the  stable  door  to  get  out  to  his  pasture. 
But  in  all  such  cases  the  knowledge  of  cause  and  effect  differs 
from  the  same  knowledge  in  man  in  one  important  particular. 
In  the  animal  it  is  always  an  individual  knowledge,  that  is,  a 
knowledge  of  individual  facts ;  while  in  man  it  is  often  a  knowl- 
edge which  has  relation  to  general  truths  or  principles. 

547.  From  the  facts  stated  in  the  last  few  paragraphs  it  is 
clear,  that  Carpenter  is  not  correct  in  saying,  that  "  the  mind 
of  man  differs  from  that  of  the  lower  animals,  rather  as  to  the 
deyree  in  which  the  reasoning  faculties  are  developed  in  him, 
than  by  any  thing  peculiar  in  their  kind"    While  there  is  much 
in  common  between  them  in  their  modes  of  mental  action,  es- 
pecially if  man  be  compared  with  other  animals  in  the  period 


360  HUMAN  PHYSIOLOGY. 

Abstract  reasoning  source  of  language  and  of  a  belief  in  a  Creator. 

of  his  infancy  and  childhood,  there  is,  as  you  have  seen,  one 
attribute  of  the  human  mind  which  is  wholly  peculiar  to  it, 
and  never  exists  in  any  degree  in  any  other  animal.  And  this 
attribute,  the  power  of  abstract  reasoning,  or  in  other  words, 
the  power  of  deducing  general  truths  or  laws  from  collections 
of  individual  facts,  constitutes  the  great  superiority  of  the  hu- 
man mind,  in  distinction  from  the  mind  of  the  brute. 

548.  It  is  this  attribute  which  is  the  source  of  language  in 
man.     This  can  be  readily  seen  by  observing  what  is  the  na- 
ture of  language.     It  is  a  collection  of  corresponding  vocal 
and  written  signs  of  an  arbitrary  character,  arranged  accord- 
ing to  certain  general  rules  or  principles.     Other  animals  do 
have  a  kind  of  language  of  a  very  limited  character.     It  is 
the  language  of  natural  signs.     It  is  composed  of  cries  and 
motions,  which  vary  in  different  tribes  of  animals,  so  that  each 
tribe  may  be  said  to  have  its  own  natural  language.     But  an- 
imals never  invent  and  agree  upon  any  arbitrary  signs,  as  is 
done  continually  by  mankind  in  the  construction  and  exten- 
sion of  language.     This  they  cannot  do,  because  abstract  rea- 
soning is  required  for  such  an  invention.     General  principles 
are  observed  in  the  construction  and  arrangement  of  arbitrary 
signs,  and,  as  I  have  shown,  brutes  know  nothing  of  principles. 

549.  This  attribute  also  is  the  source  of  man's  belief  in  a 
Creator.     If  he  had  not  the  power  of  deducing  general  truths 
from  individual  facts,  he  could  neither  discover  the  truth  that 
there  is  a  first  great  Cause,  nor  appreciate  or  even  receive  it, 
if  it  were  communicated  to  him.     Not  the  faintest  shade  of 
such  an  idea  can  be  communicated  to  any  of  the  inferior  ani- 
mals, however  high  their  mental  manifestations  may  be,  and 
simply  because  the  structure  of  their  mind  is  such  that  they 
know  nothing  of  general  principles.     Carpenter  speaks  of  the 
disposition  to  believe  in  the  existence  of  an  unseen  but  pow- 
erful Being,  which  is  found  to  be  universal  even  among  the 
most  degraded  races  of  mankind,  as  a  natural  tendency,  which 
he  seems  to  think  is  implanted  in  the  human  breast  by  the 
Creator.     But  it  appears  clear,  that  it  is  a  mere  natural  result 
of  the  exercise  of  the  power  that  I  have  just  spoken  of. 

550.  Man  differs  from  other  animals  also  in  having  a  con- 
science, or,  a  knowledge  between  right  and  wrong,  and  a  sense 
of  obligation  in  relation  to  it.     This  moral  sense  is  supposed 
by  some  to  be  a  mere  result  of  the  exercise  of  the  power  of 
abstract  reasoning.     But  others  suppose  that  the  sense  is  im- 
planted as  a  distinct  quality  or  power,  and  that  the  office  of  the 


MAN  AND   THE   INFERIOR  ANIMALS.  361 


Conscience.     None  in  animals.     Summary  of  mental  distinctions. 

reasoning  power  in  relation  to  it  is  to  bring  the  evidence  before 
it  for  its  decision.  I  shall  not  discuss  this  point,  but  will  merely 
remark  in  regard  to  this  subject,  that  there  is  no  doubt  as  to 
the  existence  of  such  a  sense  in  man.  Some  attempt  to  throw 
doubt  over  it  by  pointing  to  its  perversions,  maintaining  that  it 
is  a  mere  creature  of  circumstances,  varying  almost  endlessly  in 
different  parts  of  the  world.  But  it  would  be  just  as  rational  to 
attempt  to  show,  that  there  is  no  such  thing  as  a  sense  of  the 
beautiful  in  man,  by  appealing  to  the  evidences  of  perversions 
of  taste,  which  ignorance,  bad  education,  and  foolish  and  nov- 
elty-loving fashion  have  induced. 

551.  In  those  cases  in  animals  in  which  this  moral  sense  has 
been  supposed  to  exist,  it  is  nothing  but  slavish  fear.     It  has 
been  said  by  some  one  that  man  is  the  god  of  the  dog ;  but  it 
is  sacred  trifling  to  compare  the  attachment  of  an  animal  to  its 
master  and  its  fear  of  his  displeasure,  with  the  intelligent  regard 
of  man  for  his  Creator  as  a  holy  and  benevolent  being.     We 
ordinarily  recognize  the  distinction  between  man  and  animals, 
as  to  the  existence  of  a  conscience,  in  the  language  we  use. 
We  never  attach  the  idea  of  moral  character  to  the  acts  of  an 
animal  except  by  the  force  of  association,  and  then  only  slightly 
and  loosely.     We  are  not  apt  to  speak  of  punishing  a  dog,  for 
this  word  implies  a  moral  fault  as  the  occasion  of  the  infliction. 
We  whip  him,  sometimes,  simply  to  associate  in  his  mind  the 
smart  with  the  act  done,  so  as  to  prevent  him  from  doing  it 
again,  and  sometimes  to  vent  our  ill  feeling  for  the  harm  done 
us  on  the  poor  dog  that  has  so  innocently  done  it.     It  is  related 
of  Sir  Isaac  Newton  that  he  had  a  favorite  little  dog  called 
Diamond,  who  being  left  in  his  study,  overset  a  candle  among 
his  papers,  and  thus  burnt  up  the  almost  finished  labors  of  many 
years,  and  yet  the  philosopher  only  said,  "O  Diamond!  Dia- 
mond !  thou  little  knowest  the  mischief  thou  hast  done."     New- 
ton was  both  a  wise  and  a  good  man,  and  while  he  saw  that 
whipping  the  dog  would  do  no  good  in  preventing  any  similar 
accident  in  future,  he  had  no  ill  feeling  to  vent  on  poor  Diamond, 
who  certainly  had  a  better  arid  more  rational  master  than  most 
dogs  have. 

552.  The  mental  distinction  between  man  and  animals  may 
be  thus  summed  up.     The  animal  is  governed  by  instinct,  and 
in  the  higher  orders  by  a  kind  of  reasoning  which  is  based  upon 
mental  association.     Man  has,  in  addition  to  instinct  and  this 
lower  order  of  reasoning,  the  power  of  abstract  reasoning.     In 
the  lower  orders  of  animals  probably  instinct  rules  alone.     In 

31 


362  HUMAN  PHYSIOLOGY. 

Experience  gathered  by  animals,  but  not  transmitted. 

them  there  is  none  even  of  the  limited,  reasoning  which  we  see 
in  the  higher  animals.  They  have  a  nervous  system  with  cer- 
tain central  organs,  but  have  really  no  one  great  central  organ 
that  we  can  call  the  brain.  As  we  trace  the  animal  kingdom 
upward,  we  soon  find  that  a  brain  appears,  that  is,  such  an 
organ  as  may  be  considered  the  chief  centre  of  the  nervous  sys- 
tem. And  then,  as  we  continue  to  trace  upward  in  the  scale, 
we  find  that  the  more  intelligence  or  reasoning  there  is,  the 
more  prominent  is  the  brain  in  proportion  to  other  parts  of  this 
system.  When  we  come  to  man  the  brain  is  much  larger  than 
in  any  other  animal,  and  his  intelligence  is  not  only  greater, 
but  it  is  of  a  different  character.  Not  only  is  the  amount  of 
his  reasoning  by  association  greater  than  in  other  animals,  but 
there  is  also  superadded,  as  his  grand  distinguishing  mark,  the 
power  of  abstract  reasoning. 

553.  Instinct,  you  have  seen,  cannot  be  improved  by  educa- 
tion. It  always  acts  in  the  same  way  throughout  the  life  of  an 
animal,  and  through  the  succeeding  generations  of  the  tribe.  It 
has  no  accumulated  experience,  either  individual  or  traditional. 
But  it  is  otherwise  with  the  two  kinds  of  reasoning  power. 
These  can  be  educated,  and  they  have  an  experience.  But  here 
there  is  a  marked  difference  between  the  two  kinds  of  reason- 
ing. The  lower  kind  of  reasoning,  that  of  mere  association, 
which  is  the  only  kind  possessed  by  animals,  is  altogether  in- 
dividual, and  is  not  at  all  traditional.  However  wise  an  animal 
may  become,  there  is  no  transmission  of  his  wisdom  to  his 
posterity.  No  animal  can  start  from  a  point  of  knowledge 
gained  by  his  ancestor,  as  a  vantage  ground,  and  thus  make 
greater  advances  than  his  predecessors.  Each  animal,  in  ac- 
quiring experience  as  to  the  relations  of  cause  and  effect,  has  to 
begin  at  the  beginning,  and  learn  every  thing  for  himself.  The 
higher  form  of  reasoning,  that  which  man  alone  possesses,  is 
absolutely  essential  to  the  transmission  of  experience  from  one 
generation  to  another.  It  is  necessary  to  the  transmission  even 
of  that  experience  which  is  gathered  by  the  other  power  of 
reasoning,  as  well  as  that  which  is  gathered  by  itself.  The 
amount  of  improvement  which  can  be  effected  where  there 
is  only  the  lower  kind  of  reasoning  to  act  upon,  is  very  won- 
derful in  the  case  of  some  of  the  docile  animals.  The  dog,  the 
elephant,  the  monkey,  &c.,  are  familiar  examples.  By  the 
skillful  and  persevering  use  of  mental  association  in  the  training 
of  animals,  results  can  be  obtained,  that  resemble  very  closely 
those  which  come  from  man's  power  of  abstract  reasoning. 


MAN  AND  THE   INFERIOR   ANIMALS.  363 

The  power  of  generalization  the  basis  of  improvement  in  man. 

And  in  some  cases  the  animal  accumulates  quite  a  large  indi- 
vidual experience.  But  his  race  is  none  the  wiser  for  it.  It  ia 
none  of  it  transmitted  to  another  generation. 

554.  We  see  then  the  basis  of  improvement  in  man.     It  is 
not  his  power  of   making  inferences  merely.     The  brutes  do 
this.     It  is  his  power  of  making  general  inferences,  or,  in  other 
words,  deducing  general  laws  or  principles  from  individual  facts. 
And  as  this  power  distinguishes  man  from  the  inferior  animals, 
so  a  superior  degree  of  it  ordinarily  constitutes  the  intellectual 
superiority  of  one  man  to  another.     This  is  seen  very  readily  in 
inventions  and  discoveries.     In  the  case  of  almost  every  inven- 
tion or  discovery,  the  individual  facts  upon  which  it  is  based 
were  known  to  many  others,  perhaps  even  a  long  time  before 
the  invention  or  discovery  was  made.     The  merit  of  the  in- 
ventor or  discoverer  consists  in  having  seen  the  available  general 
truth  indicated  by  the  facts,  and  traced  out  its  application  to 
certain  objects  to  be  attained.     Thus,  to  take  a  single  example, 
dairymen  and  dairywomen  in  great  numbers  knew  the  fact, 
that  a  certain  disease,  derived  from  the  cow  accidentally  by  in- 
dividuals, prevented  them  from  taking  the  small  pox;    but 
Jenner  was  the  first  to  see,  that  here  was  developed  a  ^reat 
general  fact,  capable  of  universal  application.     And  thus  seeing 
the  wide  scope  of  the  fact,  he  collected  the  proofs  of  it,  and  de- 
vised the  means  by  which  it  could  be  made  available  to  prevent 
the  ravages  of  one  of  the  great  scourges  of  the  race.     It  was 
by  the  generalizing  power  of  his  reasoning  that  he  went  beyond 
dairymen  and  dairywomen,  and  became  the  discoverer. 

555.  It  is  interesting  to  observe  that  while  the  capabilities 
of  instinct  are  developed  rapidly,  sometimes  almost  instantane- 
ously, the  capabilities  of  the  reasoning  power  are  developed 
gradually.     Especially  is  this  the  case  with  the  higher  reasoning 
power,  that  distinguishes  man  from  the  brutes.     The  child  is 
governed  at  the  first  wholly  by  instinct ;  and  then  as  he  gathers 
knowledge  of  the  world  around  him  through  his  senses,  mental 
association  comes  into  play.     By  the  exercise  of  the  lower  kind 
of  reasoning,  which  he  has  in  common  with  animals,  he  accumu- 
lates experience  of  the  relation  of  cause  and  effect.     Thus  far 
he  is  on  common  ground  with  animals,  that  is,  those  of  the 
higher  orders,  except  that  he  adds  more  largely  to  his  experience 
from  mental  association  than  they  do.     Meanwhile  the  power 
of  abstract  reasoning  is  gradually  developed,  raising  him  up 
from  the  level  of  the  brutes,  and  introducing  him  into  compan- 
ionship with  the  whole  intelligent  creation,  even  with  God  him- 


364  HUMAK  PHYSIOLOGY. 

The  wonderful  power  of  abstract  reasoning.    Slowness  of  development  in  man. 

self,  whose  image  he  bears  in  possessing  this  attribute.  This 
power  of  generalizing  facts  is  developed  earlier  than  is  generally 
supposed.  It  is  of  course  feeble  at  first,  and  has  a  narrow 
range ;  but  it  very  early  shows  itself  sufficiently  to  indicate  to 
us  clearly,  that  the  child's  mind  differs  essentially  from  that  of 
the  brute.  And  when  disease  or  original  physical  defect  pre- 
vents its  development,  we  see  the  mental  deficiency,  and  the 
consequent  resemblance  of  the  child  in  mental  character  to  the 
inferior  animals. 

556.  When  this  characteristic  power  of  the  mind  of  man  is 
fully  developed,  its  achievements  are  often  so  wonderful,  that 
they  give  us  some  realization  of  the  great  truth,  that  man  is 
created  in  the  image  of  God.     As  we  witness  the  demonstra- 
tion of  such  facts  as  Newton  discovered,  or  the  unerring  calcu- 
lations of  an  eclipse,  or  listen  to  a  perfect  argument  as  it  develops 
grand  truths,  and  leads  us  with  a  majesty  of  thought  almost 
divine,  straight  on  to  mighty  conclusions,  we  take  in  the  full 
meaning  of  the  assertion,  that  "the  soul  is  that  side  of  our  na- 
ture which  is  in  relation  with  the  Infinite,"  and  we  see  the  folly 
of  those  dreamers  in  science,  that  look  upon  man  as  making 
merely  the  highest  order  in  the  animal  kingdom.     We  see  that 
the  chasm  between  him  and  other  animals  is  truly  "  impassable." 
We  see  that  we  are  in  a  mental  region  of  which  the  most  intel- 
ligent of  them  know  nothing — that  though  they  live  like  us, 
having  the  same  senses,  seeing  the  same  beautiful  things,  and 
hearing  the  same  voices  of  nature,  and  like  us  have  thoughts 
and  emotions  and  desires,  they  are  shut  out  from  an  upper  region 
of  thought  and  feeling  in  which  we  freely  roam,  and  from  which  we 
look  with  aspirations  unknown  to  them  to  another  world  beyond. 

557.  As  the  mental  capabilities  peculiar  to  man  are  slowly 
developed,  so  it  is  with  his  physical  frame,  and  the  powers  that 
belong  to  it.     Though  man  at  length  so  excels  all  other  animals, 
that  they  are  subject  to  his  power  as  their  master,  he  is  at  the 
first  the  most  helpless  of  all  animals.     He  is  a  long  time  "in 
the  nurse's  arms,"  and  for  years  he  is  unable  to  obtain  his  own 
food.     He  does  not  reach   the  full  strength  of  his  body  and 
mind  till  he  is  more  than  twenty  years  of  age.     He  is  in  strong 
contrast  with  other  animals  in  regard  to  this  slowness  of  devel- 
opment, they  generally  reaching  their  full  capabilities  in  a  short 
time.     But  even  among  them,  it  is  to  be  observed,  that  there  is 
a  difference  in  this  respect,  in  obedience  to  a  general  law,  that 
the  higher  the  capabilities  are,  the  slower  they  are  in  their  de- 
velopment. 


MAN   AND  THE  INFERIOR  ANIMALS.  365 

Difference  between  man  and  animals  in  physical  endowments. 

558.  The  differences  between  the  physical  endowments  of 
man,  and  those  of  the  higher  orders  of  animals,  are  often  very 
minutely  described.     But  though  strongly  marked,  too  much 
prominence  is  ordinarily  given  to  them.     They  should  be  con- 
sidered as  subordinate  altogether  to  the  mental    differences. 
Thus,  much  is  often  said  of  the  superiority  of  man  in  regard  to 
the  possession  of  a  hand,  on  which  I  have  remarked  in  various 
parts  of  this  book.     But  why  should  he  have  such  an  instrument 
given  to  him  ?     Simply  because  he  has  a  mind  which  is  not 
only  capable  of  directing  it,  but  which  needs  such  an  instrument 
to  produce  suitable  results  in  its  action  on  the  world  around. 
If  other  animals  had  a  hand  they  could  not  use  it  properly. 
1  bey  have  instruments  of  a  different  character,  of  less  various 
capabilities,  but  such  as  are  suited  to  their  wants  and  powers. 
The  same  thing  can  be  said  of  other  bodily  endowments.     They 
are  always  suited  hi  range  and  power  to  the  wants  and  mental 
capabilities  of  the  animal.     As  we  trace  out  this  general  idea, 
we  find  that  some  animals  have  some  bodily  endowments  which 
far  excel  the  same  in  man.     Thus,  some  have  greater  powers 
of  vision  and  hearing  than  he  has,  because  they  need  them. 
So,  too,  some  have  endowments  of  which  we  find  no  trace  in 
man,  as,  for  example,  the  power  of  flying.     For  the  same  reason 
most  animals  have  special  natural  means  of  defense  against  the 
attacks  of  other  animals ;  but  man  has  not,  because  he  has  no 
need  of  them,  as  by  his  ingenuity  he  can  contrive  such  means  as 
he  may  require. 

559.  The  physical  endowments  of  man  in  comparison  with 
animals  are  indeed  wonderful,  and  correspond  with  his  spiritual 
endowments,  so  far  as  gross  matter  can  compare  with  subtle 
immaterial  mind.     We  have  looked  at  these  endowments  in 
detail  in  various  parts  of  this  book.     Let  us  glance  at  the  prin- 
cipal of  them  collectively.     As  the  muscles  are  the  organs  by 
which  all  communication  between  man  and  man,  and  indeed 
all  action  upon  the  external  world  is  effected,  it  is  in  the  endless 
combinations  of  muscular  action  that  man  is  most  signally  su- 
perior to  animals  in  physical  endowment.     This  is  shown,  as 
you  have  seen,  in  the  human  hand,  whether  it  be  looked  at  as 
an  instrument  for  work  or  for  expression.     The  same  thing  we 
see  exhibited  almost  as  strikingly  in  the  muscles  of  the  voice — 
both  those  which  by  their  delicate  and  accurate  action  regulate 
the  vocal  ligaments,  and  those  which  by  their  complicated  action 
"ive  the  voice  all  its  variety  of  articulation,  especially  the  latter. 

ut  let  us  look  at  the  body  as  a  whole.     Man  walks  erect,  a 
31* 


366  HUMAN  PHYSIOLOGY. 

Beauty  of  the  human  form.    Best  shown  when  it  is  in  action. 


significant  characteristic  of  him  as  differing  from  animals.  And 
though  there  be  grace  of  movement  in  many  animals,  it  is  not 
in  any  case  to  be  compared  with  that  which  we  see  exhibited  by 
the  erect  human  form.  The  extreme  variety  of  combination  in 
the  action  of  the  muscles  in  man  is  one  cause  of  this  superiority. 
But  another  and  the  chief  cause  is  the  impress  of  beauty  given 
to  graceful  action  by  the  mind.  Almost  all  muscular  action 
speaks  to  us  a  language  that  comes  from  the  thought  and  feel- 
ing at  work  within,  even  when  it  is  unintended  ;  and  this  is  the 
source  of  a  large  portion  of  the  enjoyment  that  we  receive,  for 
the  most  part  unconsciously,  from  the  graceful  movements  that 
we  witness  in  our  fellow  men.  And  when  in  a  beautiful  and 
graceful  form  we  come  to  add  to  the  ordinary  movements  of  the 
body,  which  are  commonly,  though  improperly,  considered  as 
''  meaningless,  those  movements  which  are  distinctively  expressive 
of  thought  and  emotion,  we  are  filled  with  admiration  of  the 
wonderful  capabilities  of  the  human  frame  in  graceful  action. 

560.  The  human  form  in  repose,  when  in  its  greatest  perfec- 
tion, far  transcends,  as  a  combination  of  varied  beauty,  any 
thing  that  we  see  in  the  inferior  animals.  But  its  superiority 
in  this  respect  is  best  seen  when  the  intelligent  and  feeling 
mind  puts  it  into  action.  And  this  is  especially  true  of  those 
parts  which  are  most  engaged  in  expression — the  hand  with  its 
endlessly  varied  movements,  but  most  of  all  the  face.  It  is  in 
this  noblest  part  of  the  human  frame  that  the  soul  of  man, 
through  the  subtle  agency  of  the  nerves,  most  strikingly  imprints 
its  immaterial  qualities  upon  a  material  form,  and  exhibits  the 
highest  graces  of  motion  in  the  delicate  and  ever  varying  play 
of  the  muscles.  And  when  in  the  impassioned  speaker,  while 
the  muscles  of  the  voice  and  articulation  are  executing  their 
exceedingly  rapid  and  complicated  movements,  we  see  the  whole 
frame  in  its  motions  and  attitudes  brought  into  consonance  with 
the  burning  words  and  the  beaming  countenance,  we  take  in 
the  full  idea  of  the  adaptation  of  the  human  body  to  the  mind 
that  tenants  it.  Though  the  hand  is  commonly  spoken  of  as 
affording  the  best  illustration  of  man's  superiority  to  other  ani- 
mals in  muscular  action,  it  is  far  from  being  as  impressive  an 
exhibition  of  it  as  this  action  of  the  whole  frame.  It  is  when 
the  mind,  through  the  numberless  nerves  that  connect  it  with 
every  part  of  the  body,  brings  them  all  into  its  service  in  ex- 
pression, that  we  get  the  most  exalted  conception  of  the  excel- 
lence of  the  human  organization. 


VARIETIES   OF  THE   HUMAN   RACE.  367 

Mankind  all  the  same  species,  but  presenting  very  marked  varieties. 

CHAPTER  XIX. 

VARIETIES  OP  THE  HUMAN  RACE. 

561.  ALTHOUGH,  as  we  look  at  men  of  different  nations,  we 
find  that  there  is  a  general  agreement  in  form  and  organiza- 
tion, there  are  many  points  in  which  they  strikingly  differ  from 
each  other.     "  With  those  forms,  proportions,  and  colors,"  says 
Mr.  Lawrence,  "  which  we  consider  so  beautiful  in  the  fine  fig- 
ures of  Greece,  contrast  the  woolly  hair,  flat  nose,  thick  lips,  the 
retreating  forehead,  advancing  jaws,  and  black  skin  of  the  negro ; 
or  the  broad  square  face,  narrow  oblique  eyes,  beardless  chin, 
coarse  straight  hair,  and  olive  color  of  the  Gal  muck.     Compare 
the  ruddy  and  sanguine  European  with  the  jet  black  African, 
the  red  man  of  America,  the  yellow  Mongolian,  or  the  brown 
South  Sea  Islander ;  the  gigantic  Patagonian  to  the  dwarfish 
Laplander ;  the  highly  civilized  nations  of  Europe,  so  conspicu- 
ous in  arts,  science,  literature,  in  all  that  can  strengthen  and 
adorn  society,  or  exalt  and  dignify  human  nature,  to  a  troop  of 
naked,  shivering,  and  starved  New  Hollanders,  a  horde  of  filthy 
Hottentots,  or  the  whole  of  the  more  or  less  barbarous  tribes, 
that  cover  nearly  the  entire  continent  of  Africa ; — and  although 
we  must  refer  them  all  to  the  same  species,  they  differ  so  re- 
markably from  each  other  as  to  admit  of  being  classed  into  a 
certain  number  of  great  varieties ;  but  with  regard  to  the  pre- 
cise number,  naturalists  have  differed  materially."     Cuvier  ad- 
mitted but  three  varieties,  the  Caucasian,  Negro,  and  Mongolian. 
The  more  commonly  received  classification,  however,  is  that  of 
Blumenbach,   who  makes  five  varieties,  viz.,   the    Caucasian, 
Ethiopwn,  Mongolian,  American,  and  Malay. 

562.  The  chief  characteristic  of  the  Caucasian  variety  is  the 
fine  form  of  the  head,  it  being  nearly  oval,  as  you  view  it  from 
the  front.     It  is  also  characterized  by  a  great  range  of  varia- 
tions of  the  color  both  of  the  skin  and  the  hair.     There  has 
been  more  of  civilization  and  improvement  of  every  kind  in  this 
race  than  in  any  of  the  others.     It  is  mentally  superior  to  the 
other  races.     It  is  called  Caucasian  from  Mount  Caucasus,  from 
the  vicinity  of  which,  it  is  supposed,  it  originated.     Even  at  the 
present  day  it  is  said  that  the  characteristics  of  this  race  are 


368  HUMAN   PHYSIOLOGY. 


Blumenbach's  classification — most  commonly  received. 


most  perfectly  developed  in  the  Georgians  and  Circassians,  who 
live  in  the  neighborhood  of  this  range  of  mountains,  and  who 
are  considered  the  handsomest  people  in  the  world. 

563.  The  Ethiopian  variety  is  quite  in  contrast  with  the 
Caucasian.     The  organization  has  not  the  perfection  and  ele- 
gance which  the  Caucasian  presents,  and  it  shows  an  approxi- 
mation to  the  higher  orders  of  the  inferior  animals.     The  skull 
is  small.     The  forehead  is  retreating,  while  the  face  below  is 
projecting,  the  cheek  bones  being  prominent,   and  the  nose 
broad.     The  apparatus  of  the  senses  is  thus  fully  developed, 
while  the  brain  is  less  than  in  the  Caucasian.     The  hair  is  black, 
oily,  and  frizzled.     It  is  commonly  said  to  be  woolly,  but  it  is 
really  not  so.     Dr.  Carpenter  says  that  "  microscopic  examina- 
tion clearly  demonstrates  that  the  hair  of  the  negro  has  exactly 
the  same  structure  with  that  of  the  European,  and  that  it  does 
not  bear  any  resemblance  to  wool  save  in  its  crispiness  and  its 
tendency  to  curl."     The  skin  is  generally  black  ;  but  not  so  in 
all  the  race,  for  the  Caffirs  and  the  Hottentots  are  yellow. 

564.  The  Mongolian  variety,  of  which  the  Chinese  race  forms 
the  largest  family,  is  characterized  by  prominent  broad  cheek 
bones,  flat  square  face,  small  oblique  eyes,  straight  black  hair, 
scanty  beard,  and  olive  skin. 

565.  The  American  variety  is  characterized  by  high  cheek 
bones,  a  narrow  low  forehead,  features  large  and  bold,  except 
the  eyes,  which  are  deeply  sunken  in  large  sockets,  hair  gen- 
erally black,  stiff  and  straight,  and  complexion  varying  from  a 
crimson  brown  to  a  deep  copper. 

566.  The  Malay  variety,  which  occupies  the  Islands  south 
of  Asia,  in  the  Indian  and  Pacific  oceans,  has  not  so  well  marked 
characteristics  as  the  other  varieties.     The  complexion  is  brown, 
varying  from  a  light  tawny  to  almost  black,  the  hair  is  black 
and  thick,  the  forehead  is  low  and  round,  the  nose  is  full  and 
broad,  the  nostrils  wide,  and  the  mouth  large. 

567.  Other  classifications  have  been  made,  in  some  of  vhich 
the  human  race  is  divided  into  many  more  varieties.     Any 
classification  must  be  in  a  great  measure  arbitrary,  and  must 
be  regarded  rather  as  a  convenience,  than  as  having  the  defi- 
nite and  invariable  character  which  belongs  to  truly  scientific 
distinctions.      In  each   of  the   five  divisions    of  Blumenbach 
there  is  great  diversity.     Thus,  in  the  Caucasian  variety,  the 
English,  the  French,  the  German,  the  Irish,  &c.,  are  quite  dis- 
tinct from  each  other.     And  we  sometimes  see  very  striking 
characteristic  marks  separating  single  families  from  others.     The 


VAKIETIES   OF   THE   HUMAN   EACE.  369 

Differences  in  individuals,  families  and  nations — produced  by  similar  causes. 

varieties  of  the  race  are  thus  almost  endless,  the  lesser  differing 
only  in  degree  from  the  larger. 

568.  The  national  differences   are  evidently  produced  by 
causes  of  very  much  the  same  character  with  those  which  pro- 
duce differences  in  individuals  and  families.     And  the  question 
arises  whether  such  differences  as  those  which  Blumenbach  de- 
scribes as  marking  the  races,  are  not  produced  in  a  similar 
manner.     This  question  has  been  much  discussed,  and  there  is 
great  difference  of  opinion  in  regard  to  it.     The  great  majority 
of  naturalists  believe  in  the  unity  of  the  origin  of  the  human 
race,  and  hold  that  its  varieties  are  the  results  of  the  various 
circumstances  by  which  man  has  been  surrounded.     But  some 
suppose  that  the  different  varieties  come  from  separate  pairs 
created  by  God  in  different  localities,  and  hold  that  the  history 
in  Genesis  is  a  history  of  the  origin  of  only  one  of  the  varieties 
of  the  race.     Those  who  advocate  this  doctrine  are  few  in  num- 
ber ;  but  it  has  acquired  greater  currency  of  late,  because  one 
of  the  most  eminent  naturalists  of  the  present  day,  Professor 
Agassis,  has  espoused  it.     His  doctrine  on  this  subject  I  will 
give  as  briefly  as  possible. 

569.  All  animals,  he  asserts,  like  plants,  have  particular  lo- 
calities, for  which  they  are   fitted,  and  to  which  they  belong. 
These  zoological  provinces,  as  he  terms  them,  are  of  unequal 
extent,  some  animals  having  a  wider  range  than  others.     From 
this  general  law  of  distribution,  which  he  illustrates  with  many 
facts,  he  infers  that  the  various  animals  on  the  face  of  the  earth 
were  not  created  in  one  part  of  the  earth  and  distributed  from 
this  to  other  parts,  but  were  created  in  the  provinces  to  which 
they  belong.     This  view  of  the  subject  forces  itself  upon  the 
mind  of  the  naturalist,  as  he  observes  the  arrangement  of  the 
various  tribes  of  animals  on  the  earth's  surface.     And  besides, 
there  are  apparently  insurmountable  difficulties  in  the  way  of  a 
diffusion  of  animals  over  the  globe  by  means  of  migration.     For 
example,  we  cannot  conceive  how  the  polar  animals  could  have 
migrated  over  the  warmer  tracts  of  land,  which  they  would 
have  to  cross  according  to  this  supposition,  for  it  is  impossible 
now  to  keep  them  alive  under  such  circumstances  with  the 
greatest  precautions.     And  farther,  some  animals  of  the  same 
species,  sometimes  presenting  varieties  and  sometimes  not,  are 
found  in  different  localities  which  are  so  cut  off  from  all  com- 
munication with  each  other,  that  it  is  impossible  that  these  ani- 
mals could  migrate  from  some  one  locality  to  all  the  rest.     "  To 
assume,"  he  remarks,  "that  the  geographical  distribution  of 


370  HUMAN  PHYSIOLOGY. 

Doctrine  of  the  multiple  origin  of  the  human  race. 

such  animals,  inhabiting  zoological  districts  entirely  disconnected 
with  each  other,  is  to  be  ascribed  to  physical  causes,  that  these 
animals  have  been  transported,  and,  especially,  that  the  fishes 
which  live  in  fresh  water  basins  have  been  transported  from 
place  to  place — to  suppose  that  perches,  pickerels,  trouts,  and 
so  many  other  species  found  in  almost  every  brook  and  every 
river  in  the  temperate  zone,  have  been  transported  from  one 
basin  into  another  by  freshets  or  by  water  birds — is  to  assume 
very  inadequate  and  accidental  causes  for  general  phenomena." 
Not  only  then  were  different  species  of  animals  created  origi- 
nally in  different  localities,  but  it  is  also  true  to  a  considerable 
extent,  that  animals  of  the  same  species  occupying  different  lo- 
calities were  created  in  those  localities. 

570.  All  this  he  claims  to  be  consistent  with  scripture,  and 
with  very  good  reason.     The  account  of  the  preservation  of  an- 
imals in  the  ark,  interpreted  according  to  the  common  license 
of  language,  indicates  really  only  such  a  preservation,  as  would 
be  necessary  for  the  stocking  of  that  part  of  the  world  where 
Noah  and  his  family  were,  after  the  waters  should  subside. 
The  number  and  the  variety  of  the  animals  preserved  for  this 
purpose  would  of  course  be  very  great,  and  would,  according  to 
the  common  usage  of  language  in  narration,  be  spoken  of  in 
the  terms  used  in  the  Bible.  This  interpretation  holds  equally, 
whether  the  deluge  be  considered  as  having  been  partial  or 
universal. 

571.  The  case  being  thus  quite  clearly  made  out  in  relation 
to  animals  generally,  he  proceeds  to  trace  an  analogy  between 
them  and  the  races  of  man  in  this  respect.     He  supposes  that 
there  are  certain  zoological  provinces  for  the  different  human 
races,  as  there  are  for  the  different  species  and  varieties  of  ani- 
mals ;   and  that  these  races  were  separately  created  in  these 
provinces  with  organizations  suited  to  their  peculiar  localities. 
While  he  allows  that  climate   and  other  influences  affect  the 
varieties  of  the  human  race,  he  claims  that  they  are  not  com- 
petent to  produce  them  alone;  and  he  infers,  therefore,  that 
there  must  have  been,  as  in  the  case  of  animals,  different  original 
creations  in  the  different  zoological  districts.     He  accordingly 
claims  that  the  history  given  in  Genesis  is  a  history  of  the  origin 
of  only  one  branch  of  the  human  family.     He  does  not  sup- 
pose that  the  different  branches  constitute  different  species,  but 
are  made  varieties  of  one  species.*     He  characterizes  mankind 

*  The  difference  between  species  and  varieties  is  this.    The  distinction  of  species  rests 
upon  specific  characteristics,  that  cannot  be  changed  by  those  influences  which  tend  tc 


VAKIETIES  OF  THE   HUMAN  RACE.  871 

Most  naturalists  believe  that  the  race  came  from  one  pair. 

as  being  every  where  essentially  the  same  in  mental  character, 
and  alike  the  accountable  subjects  of  God's  kingdom,  notwith- 
standing their  multiple  origin.  It  is  in  this  respect  that  ha 
considers  them  as  being  of  one  brotherhood,  and  he  looks  upon 
the  expression  in  the  Bible,  "  made  of  one  blood,"  as  being  en- 
tirely figurative,  and  as  referring  to  "  the  higher  unity  of  man- 
kind, and  not  to  their  supposed  connection  by  natural  descent." 
I  do  not  propose  to  go  into  a  thorough  discussion  of  this 
question.  This  would  not  be  possible  in  the  narrow  limits  of 
a  chapter.  I  shall  only  present  a  general  view  of  the  chief 
facts  and  arguments  that  bear  upon  the  point  at  issue.  And 
let  us  look  at  this  subject  first  in  the  light  of  physiology  and 
natural  history. 

572.  The  great  majority  of  physiologists  and  naturalists,  as 
I  have  before  remarked,  have  thus  far  been  of  the  opinion  that 
the  human  race  came  from  one  origin,  and  that  the  varieties  of 
it  have  been  produced  by  the  various  influences  to  which  man 
has  been  subjected.     These  are  commonly  included  in  the  gen- 
eral expression,  climatic  and  other  influences.     To  be  more  par- 
ticular,  they  are — climate,  situation,  food,  clothing,   customs, 
habits,  way  of  life,  state  of  civilization.     Too  great  prominence 
has  been  undoubtedly  given  to  the  influence  of  climate.     Law- 
rence very  justly  remarks  in  his  general  conclusions  in  regard 
to  the  production  of  the  varieties  in  man  and  animals,  "  that  of 
the  circumstances  which  favor  this  disposition  to  the  production 
of  the  varieties  in  the  animal  kingdom,  the  most  powerful  is  the 
state  of  domestication."     This  word,  as  he  uses  it,  includes  all 
those  social  influences,  which  as  manifestly  affect  the  animals 
which  man  domesticates  as  they  do  man  himself.     The  analogy 
between  man  and  animals  in  relation  to  the  results  of  the  influ- 
ences referred  to  I  shall  soon  speak  of  more  particularly. 

573.  That  climatic  and  other  influences  do  have  a  very  great 
agency  in  producing  the  varieties  both  individual  and  gone  nil, 
that  we  see  on  looking  over  the  human  family,  no  one  doubts. 
The  only  question  is,  whether  they  have  produced  all  tluse 
differences — whether,  for  example,  they  have  occasioned  that 

produce  the  differences  thnt  make  varieties.  The  characteristics  of  a  species  are  orig- 
inal, while  those  of  a  variety  are  acquired.  "The  term  species,"  says  Prichard,  ''in- 
cludes only  the  following  conditions,  namely,  separate  origin  and  distinctness  of  race, 
evinced  by  the  constant  transmission  of  some  characteristic  peculiarity  of  organization. 
A  race  of  animals  or  of  plants  marked  by  any  peculiarity  which  it  has  ever  constantly 
displayed,  is  termed  a  species;  and  two  races  are  considered  specifically  different,  if  they 
are  distinguished  from  each  other  by  some  characteristic  which  the  one  cnmx.t  he  supposed 
to  have  acquired,  or  the  other  to  have  lost,  through  any  known  operutu-n  of  pnysicul 
causes." 


372  HUMAN   PHYSIOLOGY. 

Color  affected  by  climate.     Circumstances  affecting  the  form. 

very  wide  difference  that  we  see  between  the  Caucasian  and  the 
Ethiopian.  My  limits  will  not  allow  me  to  go  into  a  full  exam- 
ination of  the  influence  of  these  causes,  and  I  can  only  touch 
upon  a  few  points  in  a  very  general  way. 

574.  That  climate  has  a  great  influence  upon  the  color  of  the 
race  is  proved  by  many  clearly  observed  facts.     Tropical  heat 
always  has  a  tendency  to  produce  a  black  skin.     This  is  shown 
very  decidedly  in  the  case  of  the  Jews,  who  have  preserved  their 
characteristic  features  amid  varieties  of  climate,  and  yet  have 
their  color  altered.     Thus,  while  the  Jew  of  the  interior  of 
Europe  has  a  fair  complexion  and  light  hair,  under  the  scorching 
sun  of  India  his  hair  is  crisped,  and  his  skin  is  black.     The  ev- 
idence of  the  influence  of  climate  is  the  stronger  in  this  case, 
because  the  change  from  the  original  color  has  been  two-fold, 
For  the  original  Jew  in  Palestine  had  undoubtedly  a  dusky  skin 
and  dark  hair,  upon  which  the  temperate  climate  of  the  interior 
of  Europe,  and  the  tropical  climate  of  India  have  produced  two 
opposite  effects. 

575.  But  in  the  varieties  of  the  human  race  there  are  differ- 
ences of  form  as  well  as  of  color.     That  the  various  influences 
to  which  man  is  subjected  have  a  marked  effect  upon  his  phys- 
ical form  is  universally  acknowledged.     We  see  this  alike  in 
individuals,  families,  and  nations.     Intellectual  and  moral  influ- 
ences manifestly  have  some  agency  in  moulding  the  shape  of 
the  head  in  the  individual.     The  differences,  which  we  so  com- 
monly see  in  the  shape  of  the  head  between  the  intellectual  and 
the  ignorant,  are  not  owing  altogether  to  original  difference 
of  capacity,  but  in  part  to  education.     The  brain,  like  all  other 
organs  in  the  body,  is  influenced  in  its  development  by  the 
degree  of  activity  to  which  it  is  stimulated.     It  is  not  made  an 
exception  to  this  general  law  of  development.     Accordingly  we 
find  that  depressing  influences  tend  to  make  the  top  of  the  head, 
tlia  cerebral  part,  small,  and  the  forehead  retreating,  while  the 
face,  from  the  predominance  of  the  sensual  over  the  intellectual, 
is  rendered  relatively  too  prominent.     The  tendency  of  elevating 
influences  is  of  an  opposite  character.     And  such  influences,  thus 
operating  in  the  individual,  when  repeated  and  accumulated 
from  generation  to  generation,  produce  great  and  lasting  results. 
It  is  thus  that  a  race  becomes  either  degraded  or  elevated.     By 
a  continuance  and  accumulation  of  influences  it  acquires  either 
a  good  or  a  bad  fixed  character. 

576.  I  have  thus  spoken   of  one  class  of  causes  effecting 
changes  in  the  physical  form,  the  influence  of  which  is  manifest 


VARIETIES   OF  THE   HUMAN   EACE.  373 


Marked  tendencies  to  three  different  forms  of  the  head. 

But  there  are  changes  seen,  the  causes  of  which  we  cannot 
clearly  make  out ;  and  yet  we  know  that  they  are  occasioned 
by  the  varying  circumstances  in  which  man  is  placed.  By  the 
compound  influence  of  many  causes  combined  we  continually 
see  differences  in  the  shapes  of  various  parts  of  the  body  intro- 
duced. Family  and  national  peculiarities  are  thus  occasioned. 
The  influences  to  which  I  have  thus  referred,  some  of  which  are 
little  understood,  are  all  those  which  Mr.  Lawrence  includes  in 
the  term  domestication,  which,  as  I  have  before  said,  he  applies 
to  man  as  well  as  to  animals. 

577.  Dr.  Prichard  has  pointed  out  three  different  types  of 
form  in  the  head,  occasioned  by  three  distinct  classes  of  influ- 
ences. One  he  terms  the  prognathous,  (a  word  derived  from 
two  Greek  words  meaning  before  and  the  jaw,)  in  which  the 
jaws  project  very  prominently  forward.  This  formation  is  char- 
acterized by  the  predominance  of  the  sensual  over  the  intel- 
lectual, the  apparatus  of  the  senses  being  largely  developed, 
while  the  cerebrum  is  small,  making  the  forehead  retreating. 
The  tendency  to  assume  this  type  is  always  in  proportion  to  the 
action  of  the  degrading  influences.  "  Want,  squalor,  and  igno- 
rance," says  Carpenter,  "  have  a  special  tendency  to  induce  the 
diminution  of  the  cranial  portion  of  the  skull,  and  that  increase 
of  the  facial,  which  characterize  the  prognathous  type."  It  is 
seen  most  strongly  marked  in  the  negroes  of  the  Gold  Coast. 
In  the  pyramidal  type,  as  it  is  termed,  the  cheek  bones  are  very 
broad,  and  the  bones  above  are  so  shaped  as  to  give  the  top  of 
the  head  a  sort  of  pyramidal  form.  This  type  we  see  in  those 
tribes  that  lead  a  wandering  life — the  nomadic  races,  as  they 
are  called.  The  oval  or  elliptical  form,  which  is  seen  so  well 
marked  in  the  Caucasian  variety,  is  manifestly  the  result  of  ele- 
vating influences.  These  types  are  convertible  into  each  other. 
Thus,  the  oval  may  be  degraded  into  the  prognathous,  or  the 
prognathous  may  be  elevated  into  the  oval.  The  latter  change 
is  seen  in  the  Ethiopian,  when  in  successive  generations  he  is 
subjected  to  elevating  influences,  in  his  intercourse  with  the 
Caucasian.  And  it  is  interesting  to  observe  that  the  form  of  the 
head  is  more  readily  changed  than  the  color.  "  Thus,"  says 
Carpenter,  "  in  some  of  the  older  West  Indian  colonies,  it  is 
not  uncommon  to  meet  with  negroes,  the  descendants  of  those 
first  introduced  there,  who  exhibit  a  very  European  physiog- 
nomy ;  and  it  has  even  been  asserted  that  a  negro  belonging  to 
the  Dutch  portion  of  Guinea  may  be  distinguished  from  another 
belonging  to  the  British  settlements,  by  the  similarity  of  the 

32 


374  HUMAN   PHYSIOLOGY. 

Insensible  gradations  in  diversity.     Fixedness  of  the  varieties. 

features  and  expression  in  each,  to  those  which  peculiarly  char- 
acterized his  master's.  The  effect  could  not  have  been  produced 
by  the  mixture  of  bloods,  since  this  would  be  made  apparent 
by  alteration  of  color."  In  the  same  way  is  the  pyramidal  type 
convertible  with  the  others.  The  pyramidal  and  the  progna- 
thous are  often  mingled  together,  by  the  influence  of  vagabond 
habits  and  degrading  causes. 

578.  The  view  thus  given  of  the  operation  of  influences  in 
producing  the  varieties  of  mankind  is  strengthened  by  the  fact 
that,  as  Humboldt  says  in  his  Cosmos,  there  are  "  many  inter- 
mediate gradations  in  the  color  of  the  skin  and  in  the  form  of 
the  skull."     If  we  look  alone  at  the  extremes  in  varieties  of  color 
and  form,  we  are  of  course  disposed  to  regard  such  great  differ- 
ences as  marking  a  distinction  of  species.     But  when  we  see 
these  varieties  passing  into  each  other  by  such  insensible  grada- 
tions, and  at  the  same  time  observe  the  manifest  influence  of 
causes  upon  these  gradations,  as  in  the  cases  referred  to  in  the 
last  paragraph,  the  evidence  is  clear  to  us  that  the  varied  influ- 
ences brought  to  bear  upon  man  are  competent  to  produce  the 
varieties  of  the  race. 

579.  But  it  is  objected  that  although  climatic  and  other  in- 
fluences have  a  great  effect,  yet,  so  far  as  we  can  see,  they  only 
produce  changes  that   approximate   to  those  differences  that 
mark  the  grand  divisions  of  the  race.     They  cannot,  for  exam- 
ple, be  shown,  from  actual  observation,  to  have  effected  the 
entire  change  in  any  length  of  time  of  any  portion  of  the  Cau- 
casian race  into  the  Ethiopian,  nor,  on  the  other  hand,  of  the 
Ethiopian  into  the  Caucasian.     It  is  objected,  farther,  that  the 
peculiarities  of  the  principal  varieties  of  man  existed  in  the  early 
history  of  the  race.     This  appears  in  relation  to  the  Ethiopian 
variety  in  the  figures  found  on  Egyptian  monuments.     These 
show  that  the  peculiarities  of  the  negro  race  were  as  strongly 
marked  nearly  5,000  years  ago  as  they  are  now.     This  fixedness 
of  character  under  such  a  variety  of  influences  continued  so 
long,  it  is  claimed,  indicates  that  the  peculiarities  were  original, 
and  not  acquired. 

580.  In  reply  to  both  of  these  objections,  I  will  call  your 
attention  to  a  general  fact,  which  I  deem  to  be  very  significant 
in  its  bearing  upon  the  great  point  at  issue.     It  is  the  fact  that 
when  a  variety  is  formed  by  any  influences,  either  among  plants 
or  animals,  it  is  apt  to  remain  in  spite  of  opposing  influences. 
It  seems  to  be  easier  by  far  to  produce  a  variety,  than  to  bring 
it  back  to  the  character  of  the  original  from  which  it  came. 


VARIETIES   OF   THE  HUMAN  RACE.  875 

Influence  of  "  domestication  "  both  in  man  and  in  animals. 

Domestication  has  been  continually  producing  varieties  in  the 
animals  that  man  has  so  largely  appropriated  to  his  service,  and 
tne  varieties  once  produced,  commonly  remain.  And  the  same 
thing  is  seen  in  the  varieties  resulting  from  the  same  class  of 
influences  so  continually  in  the  human  race.  It  is  matter  of 
common  observation  that  family  and  national  peculiarities  are 
apt  to  be  perpetuated.  And  it  is  not  merely  from  a  continu- 
ance of  the  causes  from  which  they  result,  for  they  are  apt  to 
remain  even  when  strong  counteracting  influences  are  brought 
to  bear  upon  them.  Now  the  causes  which  tend  to  produce 
varieties  in  the  human  race  acted  of  course  at  the  first,  and 
were  competent  to  produce  the  most  prominent  varieties  during 
the  first  ages  of  the  race.  And  the  tendency  to  fixedness,  which 
we  see  exemplified  in  so  many  ways  in  the  varieties  of  both 
plants  and  animals,  is  sufficient  to  account  for  the  perpetuation 
of  such  marked  characteristics  as  those  of  the  Ethiopian  and  the 
Caucasian. 

581.  The  analogy  then  which  is  thus  observed  between  man 
and  the  domesticated  animals  is  a  much  clearer  and  stronger 
one,  than  that  which  Professor  Agassis  has  attempted  to  make 
out  between  man  and  animals  generally  in  regard  to  zoological 
districts.     And  the  inference  is  a  legitimate  one,  that  the  same 
influences,  that  we  see  produce  varieties  in  domesticated  animals, 
are  competent  to  produce  the  varieties  in  the  human  race,  which 
are  even  less  marked  than  some  of  those  which  we  see  in  ani- 
mals.     Varieties  are  produced   more  readily  and  in  greater 
numbers  in  animals  than  in  man,  probably  because  they  have 
less  power  of  resisting  influences  that  act  upon  them.     The  va- 
rieties of  some  of  the  domesticated  animals  are  very  numerous. 

582.  The  analogy  drawn  between  man  and  animals  in  regard 
to  zoological  districts  is  weakened  by  the  consideration,  that 
there  was  no  necessity  for  man's  being  created  in  diiferent  lo- 
calities, because  he  can  migrate  so  easily  from  one  country  to 
another.     The  necessity  existed  in  regard  to  plants  and  animals, 
but  not  to  the  same  extent  in  all.     Migration  is  easier  in  the 
case  of  some  than  in  the  case  of  others.     And  this  difference 
seems  to  have  been  acted  upon  by  the  Creator.     Accordingly, 
the  evidence  is  quite  conclusive,  that  those  animals  which  have 
been  so  universally  appropriated  by  man  to  his  service,  have 
been  diffused  from  central  points  and  have  gone  with    man, 
instead  of  being  created  in  many  localities.     This  being  the 
case,  it  is  hardly  to  be  supposed  that  man,  who  is  capable> 
through  his  ingenuity,  and  skill,  and  daring,  of  going  every 


876  HUMAN   PHYSIOLOGY, 

New  causes  occasionally  introduced  by  the  Creator.     Facts  showing  thii. 

where,  would  be  unnecessarily  created  in  different  pairs  at  differ- 
ent points  on  the  earth's  surface. 

583.  But  suppose  that  in  view  of  all  the  evidence  we  should 
come  to  the  conclusion,  that  the  climatic  and  other  influences 
are  not  the  sole  causes  of  the  differences  in  the  races,  are  we  of 
course  driven  to  the  admission  that,  as  Agassis  and  others  teach, 
there  must  have  been  created  at  the  first,  several,  we  know  not 
how  many  different  pairs  in  different  localities  ?     By  no  means. 
We  are  not  to  forget  that  the  Creator,  besides  using  influences 
of  which  we  have  no  knowledge,  (which  he  is  continually  doing,) 
can  effect  new  combinations  of  the  causes  already  existing,  or 
introduce  into  operation  entirely  new  causes.     That  he  is  from 
time  to  time  evolving  new  results  in  one  or  the  other  of  these 
ways,  or  both  of  them,  is  manifest.     The  very  common  notion, 
that  at  the  creation  all  the  causes  which  have  produced  all  the 
phenomena  that  have  been  observed  to  the  present  time,  were 
then  set  in  operation,  and  have  been  left  to  work  out  their 
results,  seems  to  be  contradicted  by  many  facts.     Most  of  the 
causes  then  set  in  operation,  it  is  true,  have  been  at  work  ever 
since.     Unless  this  were  so,  nature  would  not  exhibit  the  regu- 
larity which  it  now  does,  and  calculations  could  not  be  made 
with  such  definiteness  as  to  its  processes  from  knowledge  gained 
by  experience.     But  changes  and  irregularities  sometimes  occur 
which  must  have  been  the  result  of  new  causes.     I  shall  allude 
to  but  a  few  examples. 

584.  The  age  of  man  before  the  flood  was  much  greater  than 
it  has  been  since.     A  change  was  effected  at  that  period.     It 
was  not  a  mere  arbitrary  change,  but  such  a  change  in  the  very 
character  of  the  human  system,  that  its  capability  of  resisting 
the  tendency  to  decline  was  greatly  reduced  in  the  period  of  its 
continuance.     It  was  not  a  change  resulting  from  the  influence 
of  deteriorating  causes,  for  in  that  case  it  would  have  been  less 
suddenly  induced.     To  effect  this  change  some  new  causes  must 
clearly  have  been  brought  to  bear  upon  the  system,  making  it 
in  the  post-diluvian  a  different  system  in  some  important  respects 
from  what  it  was  in  the  ante-diluvian.     Take  a  fact  of  a  differ- 
ent kind,  indicating  a  similar  change  of  agency.     New  diseases 
from  time  to  time  appear.     This  could  not  occur  without  either 
entirely  new  causes,  or  new  combinations  of  elements  heretofore 
existing.     That  very  definitely  marked  disease,  the  small  pox, 
we  have  the  best  of  evidence,  was  not  known  to  the  ancients, 
and  is  comparatively  a  modern  disease.     It  is  impossible  to 
conceive  of  its  being  introduced  without  some  new  cause  of  a 


VARIETIES  OF   THE   HUMAN   RACE.  377 

Supposition  of  new  causes  more  probable  than  Agassis'  supposition. 

very  definite  character.  Take  now  another  fact  of  a  widely 
different  kind  from  either  of  those  to  which  I  have  alluded. 
The  earth  is  marked  all  over  with  signs  of  great  convulsions 
that  have  occurred  since  its  first  creation.  It  has  been  supposed 
till  recently  that  these  signs  all  refer  to  that  great  event  de- 
scribed in  the  Bible,  the  Deluge  of  Noah ;  but  geological 
researches  have  demonstrated  pretty  clearly  that  they  point  in 
part  at  least  to  other  previous  convulsions.  Now  these  convul- 
sions are  not  to  be  reckoned  as  a  part  of  the  regular  order  of 
nature.  They  could  not  have  resulted  from  the  ordinary  causes 
that  act  continuously.  New  causes  must  have  been  introduced 
at  the  time,  to  produce  these  unwonted  results. 

585.  It  matters  not  to  the  argument  above  indicated,  whether 
the  new  results  that  are  occasionally  developed,  come  from  a 
direct  agency  at  the  time,  or  come  from  a  chain  of  causes  set  in 
operation  a  long  time  before.     The  results  are  new  results,  and 
come  from  causes  or  combinations  of  causes,  which  differ  from 
those  that  have  produced  the  ordinary  and  regular  results  which 
we  witness  from  day  to  day  or  from  year  to  year. 

586.  Now  in  like  manner  can  we  suppose,  if  it  be  necessary, 
that  the  Creator  produced  the  varieties  of  the  human  race,  by 
adding  other  and  new  causes  to  the  ordinary  influences  to  which 
man  is  subjected.     This  is  a  much  more  probable  supposition 
than  that  of  the  advocates  of  the   multiple  origin  of  the  race. 
For  besides  accounting  satisfactorily  for  the  facts,  and  at  the 
same  time  being  consistent  with  the  record  in  Genesis,  it  is 
more  clearly  supported  by  analogical  facts  than  the  supposition, 
(for  it  is  a  mere  supposition,)  that  the  human  race  was  created 
in  different  localities.     And  farther,  this  supposition  avoids  diffi- 
culties which  attend  the  other.     For,  if  we  suppose  that  the 
race  came  from  different  pairs,  it  would  be  difficult  to  decide 
how  many  pairs  there  were.     Such  are  the  variations  of  the 
race  in  different  localities  that  there  would  be  much  disagree- 
ment as  to  the  number  of  the  representative  pairs,  and  their 
distinguishing  characteristics. 

587.  But  it  may  perhaps  be  said  in   objection,  that  I  am 
supposing  a  miraculous  interposition.     Whether  it  may  rightly 
be  termed  such  I  will  not  stop  to  consider,'  but  will  merely  re- 
mark, that  it  is  just  such  an  interposition,  or  rather,  direct  agency, 
as  is  affirmed  by  the  advocates  of  a  multiple  creation,  differing 
from  it  only  in  the  time  of  its  occurrence.     They  suppose  the 
direct  agency  of  God  to  be  put  forth  in  creation  at  different 
points,  whether  at  different  times  they  do  not  say,  and  this  is 

32* 


378  HUMAN   PHYSIOLOGY. 

The  testimony  of  the  Bible  to  be  received  as  evidence. 

really  quite  immaterial ;  and  I  suppose  the  same  direct  agency 
to  be  put  forth,  but  in  a  less  marked  manner,  to  produce  a 
change  in  what  has  been  already  created.  In  supposing  the 
direct  agency  of  the  Deity  at  all,  we  go  beyond  mere  physics ; 
and  he  surely  has  the  power  to  put  forth  this  agency  at  such 
times  as  he  pleases.* 

588.  But  the  supposition  made  above  is  not  in  my  view 
needed.     I  believe  that  the  regular,  continuous,  natural  causes, 
which  have  ever  operated  upon  man,  have  been  competent  to 
produce  all  the  varieties  of  the  race.     And  I  only  suggest  this 
supposition,  as  a  consideration  for  those  who  fail  to  see  that 
these  causes  have  been  thus  competent;    and  I  claim  that 
it  is   a  more  probable  supposition  than  the  one  offered  by 
Agassis  and  others  to  meet  the  difficulty  in  the  minds  of  such 
persons. 

589.  Thus  far  I  have  treated  this  subject  chiefly  as  one 
of  natural  history  and  physiology.     But  is  the  testimony  of 
the  Bible  not  to  be  received  as  a  part  of  the  evidence  ?     Is 
the  question  to  be  decided  wholly  on  considerations  and  facts 
drawn  from  natural  history  and  physiology  ?     This  seems  to 
be  the  view  of  some  naturalists,  though  the  great  majority  of 
them  are  disposed  to  admit  the  statements  of  Scripture  as  evi- 
dence.    It  is  true  that  the  Bible  does  not  purport  to  be  a  phi- 
losophical book.     Its  language  is  based  upon  the  principles  of 
common  and  not  scientific  usage,  and  is  so  to  be  interpreted. 
And  it  should  be  thus  interpreted  in  relation  to  the  subject  be- 
fore us.     Its  statements  on  this  subject  are  of  the  most  explicit 
character.     It  purports  to  give  an  account  of  the  origin  of  the 
race,  and  portions  of  its  history.     It  ascribes  the  corrupt  char- 
acter of  the  race  to  a  fallen  parentage.     This  connection  of  the 
general  corruption  of  the  race  with  the  fall  of  its  original  pair, 
however  divines  and  philosophers  may  differ  in  accounting  for 
it,  is  recognized  as  a  fact  throughout  the  whole  book  of  revela- 
tion.    The  testimony  is  definite,  and  is  not  to  be  mistaken. 
The  question  is,  whether  it  be  valid  testimony.     And  if  the 
Scriptural  record  be  established,  as  it  is  abundantly,  by  both 

*  There  seems  to  be  in  the  minds  of  some  naturalists  a  great  reluctance  to  admit  at  all 
the  direct  agency  of  the  Creator,  whether  it  he  exerted  in  consonance  with,  the  order  of 
nature  which  he  has  established,  or  miraculously  in  opposition  to  it.  And  they  would 
smile  skeptically  at  what  they  would  deem  the  simplicity  or  superstition  of  Hugh  Miller, 
in  referring  some  narrow  escapes  which  he  has  had,  in  pursuing  his  geological  researches, 
to  a  particular  Providence.  The  relation  of  the  agency  of  the  great  First  Cause  to  second 
causes,  it  is  true,  is  a  mysterious  subject;  but  it  implies  no  disposition  to  fathom  what  is 
unfathomable  if  we  assert  that  the  facts  are  far  from  warranting  us  in  the  belief,  that  this 
agency  has  not  been  exerted  since  the  period  of  the  creation,  but  confined  itself  to  that 
time. 


VAEIETIES   OF  THE   HUMAN"  RACE.  379 

The  unity  of  the  race  recognized  by  the  whole  scope  of  the  Bible. 

internal  and  coincident  evidence,  its  testimony  in  regard  to  the 
origin  of  the  race  is  to  be  received  by  scientific  men.  It  can 
not  be  set  aside  by  any  mere  presumptive  and  analogical  evidence 
drawn  from  physiology  and  natural  history.  If  actual  facts 
be  proved  inconsistent  with  the  Mosaic  history,  as  properly 
interpreted,  they  will  of  course  bring  discredit  upon  that  his- 
tory. No  immunity  against  a  strict  investigation  is  to  be 
claimed  for  the  Bible.  But  there  is  no  fear  of  such  an  issue  ; 
and  it  is  to  be  remembered  that  mere  analogies  are  not  facts, 
and  are  not  to  be  deemed  as  having  much  force,  especially  when 
there  is  a  question  in  regard  to  their  value  in  comparison  with 
other  analogies  that  point  to  an  opposite  conclusion. 

586.  If  the  account  given  in  Genesis  be  a  correct  account, 
as  is  generally  allowed  by  the  advocates  of  the  multiple  origin 
of  man,  and  if,  as  they  claim,  it  is  the  account  of  the  origin  of 
only  one  branch  of  the  race,  while  other  pairs  were  created  in 
other  parts  of  the  world,  they  are  driven  by  the  facts  in  the 
case  to  this  alternative.  Either  other  pairs  were  created  with 
an  original  corrupt  nature,  or  they  were  created  innocent  as 
Adam  and  Eve  were,  and  then  were  tempted  in  a  similar  man- 
ner and  with  a  similar  result.  To  claim  that  the  other  pairs 
were  made  so  like  Adam  and  Eve  as  to  constitute  with  them 
one  species,  alike  physically,  intellectually  and  morally,  without 
taking  either  of  the  suppositions  just  given,  is  to  admit  the 
truth  of  only  a  small  portion  of  the  Mosaic  account,  and  is  also 
inconsistent  with  the  existence  of  the  great  acknowledged  fact 
of  the  general  corruption  of  the  race.  So  that  it  is  evident 
that  the  unity  of  the  race,  and  the  truth  of  the  Mosaic  history, 
must  stand  or  fall  together.  And  it  is  not  the  truth  of  this 
history  merely  that  is  involved  in  this  question,  but  the  truth 
of  the  Bible  as  a  whole.  For  the  corruption  of  the  race,  which 
the  Bible  seeks  to  remove,  as  before  remarked,  is  throughout 
this  book  distinctly  referred  to  the  fall  of  man  as  recorded  in 
the  Mosaic  history  as  its  origin.  The  main  facts  of  that  record 
are  recognized  as  true  by  the  whole  scope  of  the  Bible,  what- 
ever may  be  thought  of  the  minute  particulars  of  the  narration. 
It  matters  not  then,  you  will  observe,  to  the  argument,  whether 
the  Mosaic  account  be  received  as  true  in  all  its  minutiae,  or 
whether  it  be  considered,  as  it  is  by  some,  as  a  mere  myth. 
For  the  argument  is  based  upon  the  recognition  by  the  rest  of 
the  Bible  of  the  main  facts  contained  in  the  history.  And  if  it  be 
a  myth  or  fable,  it  must  be  based  upon  these  facts,  or,  in  other 
words,  it  is  these  facts  that  it  is  the  object  01  this  myth  to  convey. 


380  HUMAN   PHYSIOLOGY. 

Distinction  between  man  and  the  higher  animals  very  definite. 


587.  I  have  thus  presented  a  summary  (for  it  necessarily  is  a 
mere  summary)  of  what  I  deem  to  be  the  proper  view  of  this 
subject     In  doing  so,  I  have  left  out  many  facts  and  considera- 
tions which  are  important,  if  we  intend  to  go  into  a  full  and 
thorough  investigation.     I  have  selected  for  your  consideration 
those  points  which  are  most  prominent  and  important.     I  have 
attempted  to  indicate  as  clearly  as  I  can  the  value  of  the  differ- 
ent prominent  arguments,  that  have  been  advanced  on  both 
sides  of  the  question.     And  from  the  views  and  facts  presented 
I  think  it  very  evident,  that  the  true  interpretation  of  the  pre- 
sumptive evidence,  drawn  from  natural  history  and  physiology, 
is  entirely  in  accordance  with  the  teaching  of  the  Bible,  viz., 
that  God  "  made  of  one  blood  all  the  nations  of  men  for  to  dwell 
on  the  face  of  the  earth."     We  are  all  one  brotherhood.     And, 
therefore,  however  debased  our  fellow  man  may  be — to  what- 
ever degree  of  degradation  the  unrestrained  corruption  of  his 
nature  may  have  brought  him — we  are  to  look  upon  him  as 
containing  the  elements  of  that  moral  and  intellectual  elevation 
which  is  attained  by  the  most  gifted  of  men.     It  is  this  view 
of  the  subject  that  imparts  dignity,  and  interest,  and  hope,  to  all 
philanthropic  efforts  to  raise  man  from  the  moral,  intellectual, 
and  physical  degradation,  to  which  sin  has  reduced  him. 

588.  Although  there  are  perhaps  none  at  the  present  time 
who  distinctly  advocate  the  doctrine,  that  the  lower  races  of 
men,  as  they  are  termed,  are  half  way  between  man  and  such 
animals  as  the  monkey  and  ourang-outang,  yet  there  is  in  some 
minds  an  indefinite  partial  admission  of  this  idea.     There  is  a 
disposition  in  some  naturalists  to  make  the  most  of  any  resem- 
blances found  between  these  races  and  animals.     The  attempt 
has  been  sometimes  made  to  show,  that  there  is  a  decided  re- 
semblance between  the  form  of  the  Ethiopian  and  that  of  the 
monkey  tribe.     But  it  has  always  failed.     It  has  been  said  that 
the  arm  of  the  negro  is  longer  than  that  of  the  Caucasian,  and 
that  in  this  respect  he  approaches  to  animals  of  this  class.     But 
the  difference  is  so  slight  that  the  analogy  fails  entirely.     And 
besides,  the  hand  of  the  negro,  the  most  important  part  of  the 
upper  extremity,  bears  no  manner  of  resemblance  to  the  imper- 
fect hand  of  the  monkey,  but  is  essentially  like  that  of  the 
European.     It  has  been  said,  too,  that  the  brain  of  the  negro  is 
like  that  of  the  monkey.     The  brain  in  any  race  or  family  of 
men  that  are  debased  and  ignorant  is  smaller  than  in  the  ele- 
vated, and  in  this  respect  alone  does  it  approach  to  that  of  the 
monkey  and  other  higher  orders  of  animals.     And,  as  I  have 


LIFE  AND  DEATH.  381 


Life,  though  various  in  its  manifestations,  in  some  senses  always  the  same. 

before  said,  there  are  certain  mental  characteristics  in  the  most 
debased  which  link  them  to  the  most  exalted  of  our  race,  creating 
an  "  impassable  chasm  "  between  them  and  the  most  intelligent 
of  animals. 


CHAPTER  XX. 

LIPE  AND  DEATH. 

589.  LIFE  is  very  commonly  spoken  of  as  being  one  thing, 
although  its  manifestations  are  exceedingly  various  in  their 
character.     In  the  simplest  growths  that  we  see,  both  in  the 
vegetable  and  the  animal  kingdoms,  the  operations  of  life  are 
in  some  respects  very  different  from  the  complicated  processes, 
that  we  witness  in  the  human  structure,  which  has  been  the 
subject  of  your  study  in  this  book.     And  yet,  as  you  have  seen 
in  the  Chapter  on  Cell-Life,  life  in  these  apparently  opposite 
cases  is  essentially  the  same.     It  is  the  same  in  its  origin.     It 
begins  always  in  a  single  cell,  whether  the  living  being  is  to  be 
minute  or  monstrous,  simple  or  complex,  a  plant  or  an  animal, 
a  creature  of  a  day,  or  a  being  destined  to  immortality.     Why 
it  is  that  from  a  simple  cell  the  vital  force,  as  it  is  termed,  can 
evolve  such  a  range  of  diversified  results  as  we  see  in  all  ani- 
mated nature,  is  one  of  the  great  mysteries  of  the  Creator.     As 
we  see  in  the  spring  time  a  bud  upon  a  tree  unfold  itself  grad- 
ually, and  develop  to  us  successively  leaves  and  flowers  and 
fruit,  it  fills  us  with  wonder,  when  we  reflect  how  much  has 
come  from  that  little  bud ;  but  when  we  go  farther,  and  think 
of  the  whole  tree  as  having  come  from  a  single  cell,  so  small 
that  it  can  be  seen  only  by  the  microscope,  the  mystery  appears 
passing  wonderful.     And  it  is  a  still  greater  mystery,  when  a 
complicated  animal  organization  is  looked  at  as  having  been 
developed  by  the  vital  force,  alike  with  all  other  living  things, 
through  a  single  cell  as  its  origin. 

590.  Life  is  not  only  always  the  same  in  its  origin,  but  it 
continues  essentially  the  same  in  its  processes.     All  the  various 
forms  which  it  produces,  both  in  the  vegetable  and  animal 
world,  are  built  and  kept  in  repair  by  cells.     All  the  functions, 
too,  are  carried  on  through  the  same  agency.     The  secretions 


382  HUMAN  PHYSIOLOGY. 

Difference  between  the  vital  force,  and  heat,  light,  and  electricity. 

and  excretions,  as  you  saw  in  §  201,  are  effected  by  constant 
successive  creations  of  numberless  cells.  Even  the  intellectual 
operations  in  the  mind  of  man  are  dependent  upon  cells  so  lono- 
as  the  mind  is  connected  with  the  body.  In  thinking,  as  well 
as  in  muscular  motion,  cells  are  worn  out,  and  must  be  replaced 
by  other  cells,  which  are  continually  supplied  by  the  vital  force. 

591.  Life  being  thus  wonderful  in  its  operations,  the  inquiry 
arises,  what  can  this  mysterious  agent  be.     With  curious  eye 
we  watch  its  workings,  but  although  we  can  learn  some  of  its 
laws,  its  nature  eludes  our  search.     Then  pressing  the  micro- 
scope into  our  service,  we  trace  it  back  to  its  hiding  place  in  a 
minute  round  cell  containing  a  fluid ;  but  simple  as  this  prison 
is  in  which  it  is  confined,  it  is  more  of  a  mystery  than  ever. 
The  vital  force,  which  begins  here,  and,  enlarging  more  and 
more  the  sphere  of  its  operations,  developes  gradually  the  simple 
or  the  complicated  living  form,  as  the  case  may  be,  has  been 
classed  by  some  with  other  forces,  the  nature  of  which  we  do 
not  understand,  as  heat,  light,  and  electricity.     But  it  differs 
from  them  entirely  in  some  important  points.     While  they  act 
in  connection  with  matter  generally,  both  organized  and  unor- 
ganized, vital  force  is  only  seen  acting  in  organized  substances. 
While  they  diffuse  themselves  through  all  kinds  of  matter  with 
more  or  less  rapidity,  the  vital  force  has  no  power  of  diffusion, 
but  is  confined  within  certain  limits.     These  limits  differ  in  the 
different  living  substances.     The  vital  force  has  the  power  of 
appropriating  matter  to  itself  within  these  limits.     It  does  this 
by  assimilation,  as  described  in  §  10.     It  has  then  the  power 
of  extension  to  a  limited  degree ;  while  the  other  forces  men- 
tioned have  the  power  of  diffusion,  in  some  respects  limitless. 

592.  Another  difference  is  this.     While  these  forces,  light, 
heat,  and  electricity,  are  lessened  in  power  by  being  diffused, 
vital  force  is  not  lessened  by  extension.     Heat,  for  example,  if 
diffused  is  lessened  at  the  point  of  its  diffusion ;  but  life  is  as 
energetic  at  its  starting  point  after  its  extension  as  before,  and 
even  more  so.     It  is,  so  to  speak,  self-generating,  while  the 
other  forces  are  mere  products.     The  vital  force  stands  peculi- 
arly alone  in  this  respect.     The  effects  too,  which  this  force 
produces,  as  it  lays  common  matter  under  contribution,  and 
fashions  it  in  such   diversified  forms,  have  an  infinitely  wider 
range  of  variety  than  the  effects  of  the  other  forces. 

593.  We  can  thus  trace  the  differences  between  the  vital  force 
or  principle  and  other  forces,  but  we  cannot,  as  I  have  before 
said,  discern  its  nature.     We  know  not  whether  it  be  one  thing. 


LIFE   AND   DEATH.  383 


Life  in  the  blood.     Vital  laws  control  the  chemical  and  mechanical. 

It  is  convenient  to  speak  of  it  as  being  so.  But  we  know  not 
but  that  it  may  be  a  compound  of  endowments,  or  tendencies 
imparted  to  matter,  and  varying  with  the  various  forms  of  living 
substances.  Some  have  supposed  that  the  vital  principle  resides 
chiefly  in  the  blood,  and  that  this  is  the  meaning  of  the  passage 
in  the  Bible,  "  the  life  of  the  flesh  is  the  blood."  That  the 
blood  has  some  vital  properties  is  certainly  true.  These  prop- 
erties are  communicated  to  it  as  it  is  made  from  the  food,  and 
fit  it  to  be  the  material  for  the  construction  and  repair  of  the 
organization.  And  it  is  simply  the  fact,  that  the  blood  is  the 
common  material  out  of  which  all  the  diversified  parts  of  the 
living  structure  are  made,  that  is  recognized  in  the  language  of 
Scripture  on  this  subject.  The  same  fact  is  embodied  in  an- 
other form  in  the  remark  of  the  French  physiologist,  that  the 
blood  is  chair  coulante,  or  running  flesh. 

594.  When  the  vital  force   appropriates  to  itself  common 
matter  in  assimilation,  it  takes  it  away  in  part  from  the  opera- 
tion of  certain  forces  which  have  had  entire  control  over  it.     As 
long  as  it  is  common  dead  matter,  it  is  wholly  subject  to  the 
laws  of  mechanics,  and  of  chemical  action.     But  when  it  be- 
comes organized  living  matter,  the  laws  of  life  take  possession 
of  it.     The  laws  of  chemistry  and  mechanics  are  not,  it  is  true, 
annulled  in  relation  to  it.     They  still  exert  their  influence,  but 
under  the  control  of  vital  laws.     The  force  of  gravity  acts  con- 
tinually upon  the  body ;  but  the  living  muscles  are  much  of  the 
time  acting  in  direct  opposition  to  it.     The  blood  circulates  on 
hydraulic  principles ;   but  the  vital  force  furnishes  the  motive 
power,  and  keeps  the  blood  from  becoming  solid  and  stopping 
up  its  channels.     Chemical  changes  are  going  on  in  the  stomach, 
the  lungs,  and  at  every  point  in  the  capillary  circulation ;  but 
they  are  modified,  controlled,  by  the  vital  principle,  and  are 
properly  termed  chemico-vital  processes. 

595.  The  human  body  is  made  of  materials  that  are  exceed- 
ingly prone  to  chemical  decomposition,  and  the  degree  of  heat 
which  is  maintained  is  such  as  to  favor  this  result ;  but  the  vital 
force  not  only  holds  the  chemistry  of  the  system  in  abeyance, 
but  even  presses  it  into  its  service.     When  life  is  destroyed,  the 
laws  of  chemistry  assume  their  full  sway,  and  the  process  of 
decay  begins.     The  very  agencies  which  served,  while  under 
the  control  of  the  vital  principle,  to  maintain  the  living  organi- 
zation, now  acting   alone  run  riot,  and  work  its  destruction. 
Thus,  that  powerful  agent,  heat,  existing  in  the  body  at  the 
point  of  98°,  is  necessary  to  the  carrying  on  of  the  processes  of 


384.  HUMAN  PHYSIOLOGY. 


Change  always  attends  life  in  action.     Life  sometimes  dormant. 

life ;  but  let  life  be  destroyed,  and  the  maintenance  of  this  de- 

free  of  heat  would  ensure  a  very  rapid  putrefaction.  So  too,  a 
egree  of  heat  which  would  rapidly  putrefy  a  dead  egg  by 
quickening  the  chemical  changes,  would  actively  stimulate  in  a 
living  egg  those  curious  vital  processes  that  produce  at  length 
the  bird.  During  intubation  the  egg  of  the  hen  is  kept  for 
three  weeks  at  a  heat  of  105°,  and  yet  when  the  chicken  is 
hatched  all  of  the  yolk  that  is  left  is  unchanged.  A  dead  egg 
would  soon  putrefy  under  such  a  temperature. 

596.  The  vital  force  exhibits  its  controlling  power  in  an  ex- 
traordinary manner  in  connection  with  that  great  force  of  nature 
to  which  I  have  just  referred.     Heat  is  very  diffusive,  and  is 
exceedingly  liable  to  change  from  varying  circumstances.     And 
yet  the  vital  force  maintains  the  heat  of  the  body  quite  uni- 
formly at  one  point,  although  the  agencies  which  tend  to  vary 
it  are  very  numerous  and  effective.     The  production  of  heat  in 
the  system  is  a  chemical  operation,  but  the  vital  principle  reg- 
ulates the  quantity  in  the  body  very  accurately,  by  providing 
for  its  escape  in  various  ways,  and  perhaps  by  curtailing  in  some 
measure  its  production. 

597.  Continual  changes  are  effected  by  the  vital  force  in  every 
part  of  the  body.     In  one  sense  death  may  be  said  to  be  taking 
place  constantly,  while  life  is  as  constantly  generated,  as  the 
useless  particles  are  separated  and  taken   away,  and  the  new 
ones  are  deposited  in  their  place.     While  these  changes  are 
going  on  the  vital  force  so  operates  as  to  maintain  the  peculiar 
shape  and  plan  of  every  part,  even  during  its  growth.     And  as 
we  look  abroad  over  all  the  diversified  forms  of  animated  na- 
ture, the  accuracy  with  which  this  force  works  in  the  prescribed 
mould  of  each  is  very  wonderful.     This  point  I  have  commented 
upon  in  the  first  chapter,  page  18,  and  will  not  dwell  upon  it 
here. 

598.  While  the  vital  force  is  in  action  there  is  constant 
change ;  but  sometimes  it  is  dormant.     A  seed  in  its  quiescent 
state  has  life  in  it,  ready  to  be  waked  into  action  by  the  proper 
excitants,  air,  warmth,  and  moisture.     Seeds  that  were  found  in 
the  excavations  of  Pompeii  have  shown  that  they  retained  their 
life  during  all  this  time,  by  shooting  forth  their  germs  as  soon 
as  they  were  exposed  to  these  natural  excitants  of  their  growth. 
One  of  the  most  interesting  cases  of  this  kind  is  related  by  Dr. 
Lindley.     "  I  have  now  before  me,"  he  says,  "  three  plants  of 
Raspberries,  which  have  been  raised  in  the  gardens  of  the  Hor- 
ticultural Society,  from  seeds  taken  from  the  stomach  of  a  man 


LIFE   AND   DEATH. 


Mysterious  connection  of  life  with  the  soul. 


whose  skeleton  was  found  thirty  feet  below  the  surface  of  the 
earth,  at  the  bottom  of  a  burrow  which  was  opened  near  Dor- 
chester. He  .had  been  buried  with  some  coin  of  the  Emperor 
Hadrian,  and  it  is  probable,  therefore,  that  the  seeds  were  six- 
teen or  seventeen  hundred  years  old." 

599.  A  similar  dormant  condition  of  the  vital  force  exists  in 
a  greater  or  less  degree.  *\s  you  saw  in  §  158,  in  the  state  of 
hibernation.     So  also,  m  cold  climates,  life  is  throughout  al- 
most the  whole  vegetable  world  dormant  during  the  period  of 
winter,  to  wake  to  greater  energy  from  the  stimulating  warmth 
of  spring.     In  the  human  body,  with  the  exception  of  some 
few  very  rare  cases,  life  is  always  in  an  active  state.     Some 
portions,  however,  of  the  system  are  a  part  of  the  time  dormant 
for  the  purpose  of  rest  and  repair.     The  brain  and  the  muscles 
sleej) ;  but  during  their  sleep  life  is  busy  in  the  formative  vessels, 
repairing  their  energies,  and  we  may  say,  their  textures  also, 
which  have  been  wasted  by  their  labor.     I  will  not  dwell  longer 
upon  this  interesting  subject,  but  in  leaving  it  I  remark,  that  it 
is  a  very  wonderful  attribute  of  the  vital  force  that  it  can,  as 
in  the  case  of  the  hibernating  warm  blooded  animals,  stop  all 
its  active  operations,  without  damage  to  the  machinery  of  life, 
and  with  such  facility  resign  itself  into  a  state  of  temporary 
inactivity. 

600.  The  most  mysterious  of  all  the  circumstances  in  regard 
to  the  vital  force  is  its  connection  in  man  with  the  immortal 
soul.     The  life  and  the  soul  are  so  intimately  connected  that 
some  have  considered  them  to  be  the  same.     But  they  are  two 
distinct  forces.    They  are  in  some  measure  indeed  antagonistic  to 
each  other.     For  the  soul,  in  using  the  machinery  of  the  nerves 
and  muscles  occasions  a  wear  and  tear  of  the  structure,  which 
it  is  the  office  of  life  with  its  numberless  cell-laboratories  to  re- 
pair.    The  soul  and  the  vital  principle  are  both  present  in  all 
parts  of  the  system,  but  not  in  the  same  sense.     The  vital 
principle  is  seen  equally  at  work  every  where.     It  has  no  great 
central  organ  from  which  it  sends  forth  its  influence.     But  the 
soul  is  especially  connected  with  the  brain,  and  by  means  of 
the  complicated  nervous  connections  of  this  organ,  it  affects 
and  is  affected  by  all  parts  of  the  system.     Its  influence  is  thus 
an  all  pervading  one.     Every  point  of  the  living  organization 
has  thus  a  sort  of  telegraphic  communication  with  the  imma- 
terial soul. 

601.  But  there  is  another  view  of  this  connection  of  the  soul 
and  the  vital  principle.     The  soiil  is  developed  in  and  with  tta 

33 


386  HUMAN   PHYSIOLOGY. 


Natural  limits  of  life.     Decay. 


living  structure.  It  is  not  created  by  itself  and  put  into  the 
body  as  a  tenant.  Its  powers  are  developed  while  the  vital 
force  developes  the  powers  of  the  physical  organization.  The 
two  processes  go  on  together.  Nay  more,  the  development  of 
the  soul  is  in  a  measure  dependent  upon  the  development  of 
the  body.  The  vital  force  exerts  a  manifest  influence  upon  the 
soul's  growth.  As  it  prepares  the  organs  for  the  use  of  the 
soul — those  organs  by  which  it  acquires  knowledge  from  with- 
out, and  thus  procures  the  stimulus  and  even  the  material  for 
its  growth — whenever  the  vital  force  fails  to  construct  these 
organs  properly,  the  powers  of  the  soul  are  not  well  developed. 
This  we  see  exemplified  in  the  idiot.  In  this  intimate  connec- 
tion of  the  soul  with  life  we  find  a  great  mystery.  Life,  a  force 
belonging  to  mere  matter,  an  endowment  of  it,  or  a  compound 
of  its  endowments — life,  that  builds  up  all  organized  substances, 
the  humblest  and  simplest  vegetable  growth,  as  well  as  that 
most  complex  of  all  living  structures,  man — life,  that  so  soon 
perishes  in  the  noblest  of  its  works  that  it  is  likened  to  the  dis- 
solving vapor — is  made  by  the  Creator  an  agent  in  developing 
an  immaterial  principle  or  being,  that  is  to  survive  the  dissolu- 
tion of  the  structure  in  which  it  is  generated,  and  is  to  live 
forever.  Strange  that  the  immortal  should  be  thus  produced 
in  the  mortal — that  the  unchangeable  and  imperishable  soul 
should  be  thus  developed  in  such  intimate  connection  with  the 
changeable  and  perishable  body.  It  is  a  mystery  which  we 
cannot  fathom. 

602.  The  vital  force,  that  is  so  busy  in  building  and  repair- 
ing so  long  as  it  lasts,  has  in  all  cases  its  natural  limit ;  and  in 
the  case  of  the  human  system  it  seldom  fully  reaches  this  limit. 
The  diversified,  and  complicated,  and  beautiful  structures  which 
it  evolves,  if  saved  from  accident  till  the  natural  period  of  de- 
cline comes,  lose  their  vigor  and  beauty,  and  at  length  die  and 
are  given  up  to  the  action  of  the  common  laws  of  chemistry, 
which  the  vital  force  has  so  long  resisted  and  controlled.     The 
structures  then  decay,  and  the  particles  are  dissipated,  perhaps 
to  be  united  again  to  other  structures. 

603.  The  death  of  the  body  is  not  ordinarily  complete  at 
the  moment  when  what  we  term  death  occurs.     Though  as  a 
whole,  as  a  system  of  organs,  the  operations  of  life  are  at  an 
end,  yet  there  is  some  degree  of  life  in  some  parts,  and  there 
may  be  in  all  parts  of  the  body.     The  beard  and  nails  even, 
may  grow.     Some  of  the  organs  may  secrete  their  fluids — the 
liver  its  bile,  and  the  stomach  its  gastric  juice.     Some  of  the 


LIFE   AND  DEATH.  387 


Systemic  and  molecular  death.    Death  beginning  in  the  heart,  and  in  the  lungs 

properties  of  life,  too,  manifestly  still  remain.  The  irritability 
of  the  muscles,  which  is  strictly  a  vital  property,  as  it  never 
belongs  to  common  dead  matter,  still  appears  on  the  applica- 
tion of  excitants.  It  was  the  contraction  of  the  muscles  in  the 
leg  of  a  dead  frog  on  the  accidental  application  of  a  stimulus, 
that  led  Galvani  to  his  grand  discovery.  And  it  is  through 
this  vital  property  that  the  culprit  who  has  been  hung  can  be 
galvanized  into  apparent  life.  Death  then  may  be  said  to  be 
of  two  kinds — systemic,  that  is,  the  death  of  the  body  as  a 
whole,  a  system  of  organs — and  molecular,  that  is,  the  death 
of  the  individual  molecules  or  particles  which  compose  the 
body.  Death  can  be  said  to  be  complete  only  when  the  laws 
of  life  have  resigned  their  power  over  these  molecules,  and  the 
laws  of  purely  chemical  action  have  taken  their  place.  When 
this  change  occurs,  the  process  of  decay,  which  is  strictly  a 
chemical  process,  begins. 

604.  It  will  be  interesting  to  notice  here  the  modes  in  which 
systemic  death  occurs.     There  are  three  great  systems  in  the 
body,  each  of  which  is  immediately  essential  to  the  continuance 
of  life — the  system  of  the  circulation,  the  respiratory  system, 
and  the  nervous  system.     And  we  may  speak  of  death  as  be- 
ginning in  any  one  of  these  systems  when  the  cause  of  death 
acts  primarily  upon  it.     I  will  notice  some  examples  under  each 
head. 

605.  If  a  large  quantity  of  blood  be  lost,  so  large  as  to  result 
fatally,  death  in  this  case  obviously  begins  in  the  circulation. 
The  heart  not  being  supplied  with  the  quantity  of  blood  that 
usually  flows  through  it,  becomes  more  and  more  feeble  in  its 
action,  till  it  at  length  ceases  to  beat.     When  a  large  aneurism 
bursts,  it  is  the  sudden  drain  from  the  circulation  that  destroys 
life. 

606.  Any  thing  which  to  any  great  extent  prevents  the  air 
from  entering  the  lungs  may  cause  death  to  begin  in  the  respt 
ratory  system.     This  may  be  done  by  three  classes  of  causes. 
1st.  Causes  that  act  upon  the  large   air  passages.     Example*, 
of  this  class  of  causes  are  strangling,  smothering,  drowning, 
&c.     In  croup  the  principal  cause  of  death  is  the  prevention 
of  the  free  passage  of  air  through  the  windpipe  into  the  lungs. 
2d.  Causes  which  act  upon  the  walls  of  the  chest.     If  a  bank 
of  earth  fall  upon  a  man,  though  it  leave  his  head  clear,  so  that 
the  air  passages  are  unobstructed,  he  cannot  breathe,  because 
his  chest  is  held  as  if  in  a  vice.     A  man  came  near  dying  from 
this  cause,  who  was  having  a  cast  taken  of  the^upper  part  of 


388  HUMAN   PHYSIOLOGY. 


Death  beginning  in  the  nervous  system. 


his  body.  If  the  muscles  of  respiration  were  to  be  paralyzed, 
death  would  ensue,  just  as  it  does  when  they  are  prevented  from 
acting  by  other  causes.  3rd.  Causes  acting  upon  the  lungs. 
Disease  may  occasion  an  amount  of  obstruction  in  the  very 
substance  of  the  lungs  sufficient  to  cause  death.  It  does  so  by 
preventing  the  introduction  of  the  air  into  the  minute  air  vessels, 
where  the  air  revivifies  the  blood.  The  obstruction  is  just  as 
effectual  in  this  case  as  it  is  where  it  occurs  in  the  large  air 
passages. 

607.  When  death  occurs  from  a  blow  upon  the  head  as  the 
immediate  result  of  the  shock,  we  have  an  example  of  death 
beginning  in  the  nervous  system.     But  the  cause  may  act  upon 
this  system  in  some  other  quarter.     A  blow  at  the  pit  of  the 
stomach,  for  example,  may  so  shock  the  whole  nervous  system 
as  to  stop  at  once  the  operations  of  life.     Some  poisons,  too,  as 
opium,  destroy  life  by  their  influence  upon  this  system.     Very 
extensive  burns  give  a  shock  to  the  nerves  from  which  they  do 
not  rally.     The  same  can  be  said  of  other  injuries  when  there 
is  no  recovery  from  the  first  shock.     Powerful  medicines,  im- 
properly given  in  cases  of  disease  disposed  to  prostration,  may 
depress  the  nervous  system  to  a  point  from  which  it  may  never 
revive.     Cold  destroys  life  mostly  by  the  benumbing,  paralyzing 
influence  which  it  exerts  upon  the  nerves. 

608.  Though  we  thus  classify  the  modes  of  death,  in  the 
great  majority  of  cases  death  is  a  complex  event,  resulting  from 
a  concurrence  of  causes.     It  is  so  even  when  the  disease  is  not 
of  a  complicated  character.     Take,  for  example,  a  case  of  pure 
uncomplicated  consumption,  in  which  all  the  organs  but  the 
lungs  are  in  a  healthy  state  to  the  end.     The  whole  system 
becomes  at  length  exhausted  by  the  disease.     If  this  exhaustion 
alone  be  the  cause  of  death,  then  we  may  say  that  it  is  an  ex- 
ample of  death  beginning  in  the  nervous  system.     But  if  the 
obstruction  in  the  lungs  to  the  admission  of  air  in  the  air-cells 
be  the  cause,  it  is  a  case  of  death  beginning  in  the  respiratory 
system.     Generally  in  such  cases  death  results  from  the  two 
causes  combined,  and  it  is  often  difficult  to  determine  which  is 
the  more  prominent  cause. 

609.  The  signs  of  death  are  so  clear  that  there  is,  with  very 
few  exceptions,  no  mistake  in  regard  to  the  occurrence  of  the 
event.     The  stories  that  are  related  about  burying  alive  are 
most  of  them  unfounded.     The  apprehensions  created  by  them 
in  the  minds  of  some  persons  have  led  them  to  insist,  that  no 
body  ought  to  be  committed  to  the  grave,  till  the  most  infalli- 


LIFE  AND  DEATH.  389 


The  signs  of  death.    Death  as  viewed  by  the  Physiologist,  and  the  Christian. 

ble  sign  of  death,  putrefaction,  has  appeared.  That  we  should 
wait  for  the  appearance  of  this  sign  in  all  cases  in  which  there 
is  a  shadow  of  doubt,  I  will  allow.  But  the  cases  are  exceed- 
ingly rare  in  which  we  cannot  determine  the  reality  of  death 
long  before  this  sign  shows  itself.  Our  decision  is  not  made 
up,  it  must  be  observed,  merely  from  the  signs  of  death.  All 
the  circumstances  of  the  case  are  taken  into  view — the  disease, 
its  progress,  its  symptoms,  and  the  events  of  the  last  hours  of 
the  patient.  With  this  evidence  before  us,  we  absolutely  know, 
in  all  ordinary  cases,  that  death  has  occurred  when  the  respi- 
ration and  the  circulation  have  ceased.  And  in  the  exceed- 
ingly few  cases  in  which  there  is  any  reason  to  doubt  on  that 
point,  there  is  always  something  which  will  attract  the  attention 
and  excite  the  curiosity  of  some  one,  unless  there  be  stolid  in- 
difference and  the  most  absolute  lack  of  intelligence.  In  such 
cases  there  is  always  something  strange — the  circumstances 
attending  the  cessation  of  the  respiration  and  circulation  are 
singular,  and  the  signs  of  death  are  not  complete  and  in  their 
proper  order  of  succession.  Whenever  there  is  for  these  reasons 
any  doubt  as  to  the  reality  of  the  apparent  death,  the  strictest 
watch  should  be  maintained  till  the  signs  of  commencing  putre- 
faction appear.  With  this  simple  rule  of  prevention  burying 
alive  need  never  to  occur. 

610.  The  investigations  of  physiology,  as  you  have  seen,  end 
with  the  death  of  the  body.  It  can  give  us  no  light  on  the 
question  as  to  what  may  be  beyond  this  life.  Although  the 
physiologist  studies  the  human  structure  not  merely  as  an  or- 
ganization instinct  with  life,  but  also  as  the  wonderful  machinery 
through  which  a  reasoning  soul  acts  and  is  acted  upon  in  this 
state  of  being,  yet,  as  a  physiologist,  he  knows  not  that  the 
soul  survives  the  death  of  the  body.  He  knows  not  but  that 
it  is  a  mere  endowment  of  matter,  as  life  probably  is,  and  so 
perishes  in  the  hour  of  dissolution.  He  may  indeed  conjecture 
that  such  exalted  faculties  which  are  in  this  world  susceptible 
of  such  high  cultivation,  instead  of  being  destroyed  with  the 
body,  are  destined  to  still  farther  development  in  another  state 
of  existence.  But  what  is  mere  conjecture  'to  him  as  a  Physi- 
ologist, is  made  fact  to  him  as  a  Christian.  The  eye  of  his 
faith  sees  an  immortal  spirit  rise  from  the  dying  body,  and  he 
realizes  the  truth  of  the  sublime  declaration,  that  "death  is 
swallowed  up  of  victory." 


890  HUMAN   PHYSIOLOGY. 

Sources  of  our  knowledge  of  hygiene. 


CHAPTER  XXL 

HYGIENE. 

611.  IT  seems  appropriate  that  the  concluding  chapter  of 
this  book  should  be  on  Hygiene.     After  having  considered 
the  construction  of  the  machinery  of  the  human  system  and 
the  uses  which  the  mind  makes  of  it,  one  naturally  inquires 
what  are  the  conditions  on  which  the  full  development  of 
this  complicated  machinery  and  its  daily  repair  depend. 

612.  The   principles    and   rules   of   Hygiene  are  to   be 
learned  from  two  sources.     1.  They  are  to  be  learned  from 
Physiology.     As  we  observe  the  functions  of  the  different 
organs,  we  can  learn  what  those   circumstances  are  which 
favor  their  due  performance,  and  what  those  are  which  in- 
terfere with  it.     2.  They  are  to  be  learned,  also,  by  observ- 
ing  the    effects  of  those    agencies    which    are    known    to 
interfere  with  the   functions  and  to  produce  disease.     An 
exemplification  of  these  two  modes  of  learning  the  principles 
of  Hygiene  in  relation  to   a  single  point  will  suffice.     The 
study  of  the  physiology  of  the  chest  shows  us  that  nature 
has,  in  the  construction  of  its  framework,  especially  provided 
for  giving  ample  room  to  the  lungs ;  and  so  we  deduce  a 
law  of  Hygiene,  that  the  chest  should  not  in  any  way  suffer 
compression.     This  is   the  first  mode.     But  the  same  law 
can  be  deduced  by  the  second  mode,  that  is,  by  observing 
the  results  of  compression  of  the  chest. 

613.  Rules  of  hygiene  generally  have  but  little  practical 
influence,  unless  the  physiological  facts  upon  which  they  are 
based  are  understood.     Although  the  evil  effects  of  their 
violation  may  be  vividly  portrayed,  and  even  illustrated,  as 
in  the  case  of  the  chest,  by  engravings,  the  impression  upon 
the  mind  is  by  no  means  as  thorough  and  practical,  as  when 
the  same  lesson,  is  enforced  by  a  clear  knowledge  of  the 
functions  and  arrangements  of  the  organs  and  the  conditions 
necessary  to  their  healthy  action.     Physiology,  therefore, 
should  be  studied  as  preparatory  to  a  proper  appreciation  of 
Hygiene. 

614.  Not  only  is  a  knowledge  of  Physiology  essential  to 
a  proper  appreciation  of  the  rules  of  Hygiene,  but  in  many 


HYGIENE.  391 


Hygiene  of  digestion.     Quantity  of  food  to  be  eaten. 


cases  they  cannot  be  fully  understood  in  their  varied  appli- 
cation without  such  a  knowledge.  With  the  very  partial 
and  superficial  knowledge  of  Physiology  that  is  usually 
communicated  with  Hygiene,  these  rules  are  for  the  most 
part  mere  arbitrary  rules.  And  just  so  far  as  the  principles 
on  which  they  are  based  are  not  understood,  is  there  a 
liability  to  mistake  their  application  under  various  circum- 
stances. 

615.  In   considering   the  subject  of  hygiene,  the  natural 
division  of  Physiology,   stated   in  §  57,  should  be  kept  in 
mind.     There  is  a  hygiene  relating  to  the  construction  of  the 
machinery  of  the  body,  and  there  is  also  a  hygiene  relating 
to  the  uses  of  this  machinery.     Besides,  each  organ  has  to  a 
certain  extent  its  own  hygiene.     And  yet,  as  all  the  organs 
are  connected  more  or  less  together  in  sympathetic  action, 
there  is  a  general  hygiene  of  the  system.     I  shall  observe 
for  the  most  part  the  same  natural  order  that  I  followed  in 
developing  the  subject  of  Physiology.     I  shall  first  treat  of 
the  hygiene  of  the  construction  and  repair  of  the  system — 
that  is,  the  hygiene  of  digestion,  circulation,  respiration,  and 
formation  and  repair.     You  can  recur  to  a  summary  of  these 
functions  given  in  §  69.     I  shall  then  pass  to  the  considera- 
tion of  the  hygiene  of  the  uses  of  the  machinery  thus  con- 
structed and  kept  in  repair. 

616.  Many  of  the  points  in  the  hygiene  of  the  digestive 
organs  have  been  already  noticed  in  the  physiology  of  diges- 
tion.    I  need  say  nothing  more  in  addition  to  what  is  said 
there  of  the  importance  of  the  thorough  mastication  of  food, 
and  of  its  having  a  due  amount  of  saliva  mingled  with  it ; 
of  the  evils  resulting  from  eating  too  fast,  from  eating  be- 
tween meals,  and  from  eating  a  great  variety  of  food  ;  and 
of  the  influence  of  exercise  upon  the  process  of  digestion. 
There  are  some  other  points,  however,  that  remain  to  be 
noticed. 

617.  No  very  precise  rules  can  be  given  as  to  the  quan- 
tity of  food  that  is  proper  to  be  eaten.     But  a  consideration 
of  the   physiological   principles  of  digestion  suggests  rules 
that  are  sufficiently  definite  for  practical  purposes.     There 
must  be  such  an   amount  of  food  as  will  furnish  sufficient 
chyle  to  keep  the  blood,  the  building  material  of  the  body, 
in    proper  quantity.      The  question   arises,   how  we  shall 
know  what  amount  of  food  is  requisite  for  this  purpose 
Fortunately,  the  want  of  the  system  and  its  supply  are  com 


392 


HUMAN   PHYSIOLOGY. 


Mistakes  as  to  quantity  of  food.    Length  of  intervals  between  meala. 


monly  quite  accurately  indicated  by  the  sensations  as  stated 
in  §  87.  The  proper  hygienic  rule  then  on  this  point  is, 
that  we  should  cease  to  eat  when  the  sensations  created  bv 
the  want  of  the  system  are  removed — that  is,  when  the 
hunger  is  appeased,  and  the  accompanying  feeling  of  discom- 
fort is  succeeded  by  a  feeling  of  agreeable  ease. 

618.  But  there  are  mistakes  often  made  in  regard  to  these 
sensations.     They  may  be  prevented  from  making  a  true 
report.     Thus,  when   eating  is  done  too  rapidly,  more  food 
than  is  needed  may  be  introduced  into  the  stomach  before 
the  sensation  of  ease  and  satisfaction  is  experienced.     It  is 
only  when  suitable  time  is  given  to  mastication,  and  the 
food  is  rather  gradually  introduced,  that  this  sensation  forms 
the  proper  limit  of  eating.     Again,  there  is  a  very  common 
mistake  in  substituting  the  feeling  of  fulness  for  the  sensation 
alluded  to,  as  indicating  the  time  for  ceasing  to  eat.     Those 
who  adopt  this  false  rule  generally  make  the  stomach   tc 
bear  as  much  as  it  can  without  absolute  discomfort,  and 
many  daily  overreach  this  point.     The  result  is,  that  this 
organ  soon  gives  out  under  this   daily  overworking  ;  or,  if 
the  stomach  be  a  strong  one,  an  injurious  repletion  is  pro- 
duced in  the  system.     Even  in  the  latter  case,  the  stomach 
at  length  gives  out,  and  becomes  the  seat  of  disease.    But  it 
is  astonishing  how  much  labor,  in  the  work  of  digestion,  this 
organ  will  perform  in  some  cases. 

619.  Too  little  food   is  sometimes  taken.      Poverty  is 
commonly  the  cause.     But  sometimes  it  arises  from  false 
notions ;  as,  for  example,  the  notion  that  the  quantity  of 
food  should  be  regulated  by  weight,  or  the  more  common 
notion,  that  we  should   rise  from  a  meal  with  some  amount 
of  appetite  remaining.     The  result  is,  that  there  is  not  a 
sufficient  supply  of  chyle  to  meet  the  wants  of  the  system. 
The  wear  and   tear  create  a  demand  which  is  greater  than 
the  supply,  and  the  body  therefore  loses  its  fulness  and  its 
vigor. 

620.  In  determining  the  length  of  the  intervals  between 
the  meals,  we  should  have  regard  to  the  time  required  for  the 
completion  of  the  process  of  digestion,  and  to  the  wants  of 
the  system.     Some  articles  are  digested  more  rapidly  than 
others,  but  it  commonly  requires  from  three  to  four  hours 
to  complete  the  digestion  of  a  meal.     When  the  system  is 
in  a  state  of  action,  its  want  of  food,  as  indicated  by  its 
sensations,  shows  itself  a  little  time  after  the  completion  of 


HYGIENE.  393 


Begularity  of  meals.    Quality  of  food.    Influence  of  the  mind  on  digestioa 

the  process  of  digestion.  The  interval,  then,  between  the 
meals  should  not  vary  much  from  four  hours.  If  it  be  made 
longer  than  five  hours,  some  degree  of  exhaustion  results ; 
and  if  it  be  less  than  three  hours,  disturbance  of  the  diges- 
tive process  may  occur,  from  having  the  digestion  of  one 
meal  begin  before  that  of  the  previous  one  is  fairly  finished. 

621.  It  is  important  that  the  meals  should  be  eaten  at 
regular  periods  from  day  to  day.     For  the  stomach,  with  its 
times  of  work  and  of  rest,  naturally  contracts  regular  habits, 
a  disturbance  of  which  is  injurious.    This  obedience  to  habit 
in  this  organ  is  manifest  whenever  any  change  is  made  in 
the  time  of  eating. 

622.  The  question  is  often  asked,  whether  such  and  such 
an  article  "  is  healthy,"  as  if  there  were  essentially  different 
degrees  of  suitableness  in  different  articles  of  diet.     So  far 
as  digestion  is  concerned,  any  article  is  healthy  to  any  in- 
dividual whose  stomach  can  digest  it  without  difficulty.    An 
article  may  be   perfectly  healthy  to  one,  and  unhealthy  to 
another.     There  are  sometimes  wide  differences  in  this  re- 
spect, owing  to  unaccountable  peculiarities.     But  even  in  re- 
gard to  ordinary  differences,  the  question  as  to  the  propriety 
of  any  article  of  food  is  wholly  an  individual  question. 

623.  Our  food  should  be  varied  in  the  different  seasons 
of  the  year  to  a  greater  extent  than  is  commonly  done.     In 
the  warmer  seasons  it  needs  to  be  less  stimulating,  less  heat- 
producing  than  in  the  colder  seasons.     The  fruits,  each  in 
its  season,  should  form  regularly  quite  a  large  proportion 
of  our  food  in  the  warmer  months.     If  used  thus,  and  not 
irregularly,  as  is  commonly  the  case,  they  will  tend  to  pre- 
vent, rather  than  induce,   the  complaints  peculiar  to  that 
portion  of  the  year. 

624.  The  state  of  the  mind  has  much  influence  on  the 
digestive  organs.     This  is  sometimes  strikingly  exhibited  in 
the  loss  of  appetite  on  the  sudden  reception  of  bad  news. 
It  is  also  seen  in  the  influence  of  continued  sorrow  upon  the 
appetite  and  the  digestion.     It  is  not  strange,  then,  that  one 
of  the  prominent  causes  of  dyspepsia  is  mental  disturbance 
or   depression.      And    a  cheerful   mind    is  very  properly 
deemed  to  be  essential  to  easy  and  thorough  digestion. 

625.  In  order  to  understand  fully  the  hygiene  of  respira- 
tion, it  must  be  borne  in  mind,  that  the  great  object  of  this 
function,  as  stated  in  §  131,  is  to  bring  the  air  into  all  the 
minute  air-oells  of  the  lungs,  that  it  may  change  the  blood 


394:  HUMAN   PHYSIOLOGY. 

Compression  of  the  chest.    Importance  of  a  good  supply  of  pure  air. 

which  is  sent  there  for  this  purpose.  Anything,  then,  which 
interferes  with  the  free  introduction  of  the  air  into  these 
cells  is  a  palpable  violation  of  the  laws  of  health.  And  yet 
this  interference  is  so  commonly  practised,  that  it  is  one  of 
the  prominent  causes  of  disease. 

626.  This  interference  is  effected  in  two  ways.     It  is  done, 
first,  by  mechanical  compression   of  the  chest.     Although, 
as   I  have   shown  in  the  chapter  on  the  Respiration,  there 
are  special  pains  taken  by  the  framer  of  our  bodies  to  pro- 
vide, in  the  construction  of  the  chest,  for  the  free  introduc- 
tion of  air  into  the  lungs  under  all  circumstances,  this  is 
often  prevented  by  certain  prevalent  modes  of  dress.     It 
must  be  observed  that  in  the  arrangement  of  the  chest,  a 
free  motion  of  its  walls  in  the  expansion  of  the  lungs  is  con- 
templa.ted.      The  dress,  therefore,  should  always  be  so  loose  as 
to  admit  of  this  free  motion.     If  it  is  not,  the  air  is  not  freely 
admitted  to  all  the  air-cells,  and  therefore  the  blood  is  not  as 
fully  changed,  as  nature  requires ;  and  the  health  is  impaired 
just  in  proportion  to  the  degree  in  which  the  due  expansion 
of  the  chest  is  prevented.     I  have  said  so  much  on  the  re- 
sults of  this  compression  of  the  chest  in  the  chapter  on 
respiration,  both  in  this  book  and  in  my  "  First  Book  on 
Physiology,"  that  I  will  only  say  here,  that  in  this  country 
it  is  one  of  the  most  prominent  causes  of  disease  among 
females.     It  not  only  produces  disease  in  the  lungs,  but,  by 
preventing  these  organs  from  effecting  fully  the  requisite 
change  in  the  blood,  it  impairs  the  quality  and  lessens  the 
quantity  of  this  building  material,  and  thus  diminishes  the 
nutrition  and  the  vigor  of  the  system,  and  therefore  renders 
it  liable  to  a  great  variety  of  diseases,  especially  those  of 
which  debility  is  a  prominent  characteristic. 

627.  The  free  introduction  of  pure  air  into  the  lungs  is  in- 
terfered with,  secondly,  by  cutting  off  its  supply.     As  you 
learned  in  the  chapter  on  respiration,  the  oxygen  of  the  air 
is  used  up  in  large  quantities  by  the  lungs,  and  the  carbonic 
acid  gas  thrown  off  takes  its  place.  If,  therefore,  there  be  not 
sufficient  provision  for  the  supply  of  fresh  relays  of  pure  air, 
a  mixture  of  air  and  carbonic  acid  gas  will  be  introduced 
into  the  lungs  at  every  breath,  so  that  there  will  not  be 
sufficient  oxygen  to   effect   thoroughly  the   change   in    the 
blood.     In  this  respect,  therefore,  the  result  is  the  same  as 
when  too  little  air  is  admitted  by  reason  of  compression  of 
the  chest.     A  portion  of  the  requisite  quantity   of  pure  air 


HYGIENE.  395 


Bad  results  of  defective  aeration  seldom  appreciated.    Hygiene  of  the  circulation 

is  shut  out,  irf  one  case  by  diminishing  the  capacity  of  the 
chest,  and  in  the  other  by  having  the  lungs  in  part  occupied 
by  carbonic  acid  gas. 

628.  The  influence  which  this  defective  aeration  of  the 
blood,  occasioned  by  these  two  causes,  exerts  upon  the 
health,  is  seldom  appreciated.  For  unless  the  deficiency  be 
very  great,  no  immediate  obvious  result  is  produced.  But 
though  the  deficiency  may  be  comparatively  small,  if  it  be 
continued  from  day  to  day  for  a  long  time,  the  aggregate 
result  of  this  steady  depressing  influence  is  a  serious  one. 
The  destruction  of  health  and  of  life  that  comes  from  this 
imperceptible  agency  in  every  community  is  vast  in  amount. 
But  most  persons  seem  to  be  insensible  to  this  fact.  They 
need  a  narrative  of  such  a  destruction  of  life  as  occurred  in 
the  Black  Hole  at  Calcutta,  to  convince  them  that  a  consider- 
able quantity  of  fresh  air  is  required  by  every  pair  of  lungs. 
And  it  is  only  by  a  description  of  an  examination  after 
death  of  some  one  who  has  been  killed  outright  by  extreme 
compression  of  the  chest,  that  they  can  be  made  sensible  of 
the  need  that  the  lungs  have  of  the  room  that  nature  has 
given  them.  And  even  then  the  impression  seems  to  be  a 
momentary  one.  If  all  the  injury  that  is  done  by  defective 
aeration  of  the  blood  could  be  visibly  traced  out,  we  should 
then  realize  the  necessity  of  having  just  as  many  of  the 
air-cells,  those  little  chemical  laboratories,  as  nature  de- 
signed, and  of  keeping  them  well  supplied  with  the  fresh  air 
which  they  require  for  the  life-giving  work  that  they  per- 
form. 

629.  The  hygiene  of  the  circulation  need  not  detain  us 
long.  The  office  of  the  organs  of  the  circulation  is  to  circu- 
late the  blood,  the  building  material,  everywhere.  They 
never  rest  from  their  work.  But  they  work  more  actively 
when  the  muscular  system  is  in  action  than  when  it  is  at 
rest.  As  one  lies  in  bed,  the  circulation  goes  on  steadily, 
but  quietly.  But  on  rising  and  moving  about,  the  circula- 
tion becomes  more  active.  Not  only  does  the  heart  beat 
more  quickly,  but  the  capillaries  in  every  part  of  the  body 
increase  their  action.  And,  as  more  blood  is  carried  to 
every  part,  there  is  more  done  everywhere.  We  see  this 
in  the  skin,  in  the  increase  of  the  perspiration  on  exercise. 
When  the  muscular  effort  is  very  great,  the  excitement  of 
the  circulation  is  violent  and  tumultuous.  The  heart  beats 
strongly  and  rapidly,  and  tbe  flushed  face  shows  how 


HUMAN"   PHYSIOLOGY. 


Exercise  necessary  to  health. 


active  is  the  circulation  in  its  extreme  vessels,  the   capil- 
laries. 

630.  The    occasional   excitement   by   active   exercise   is 
absolutely  essential  to  the  proper  development  of  the  body. 
It  may  sometimes,  indeed,  maintain  its  proper  bulk  in  a  con- 
tinued state  of  muscular  inaction  ;  but  its  textures  will  not 
have  the  requisite  strength  and  tone.     That  they  may  have 
these  qualities,  it  is  necessary  that  the  blood  be  often  pump- 
ed into  their  capillaries  with  the  force  that  is  given  to  the 
heart  by  active  exercise.     It  is  not  the  muscles  alone  that 
are  rendered  stronger  and  firmer  by  exercise,  but  the  same 
effect  is  produced  in  all  the  textures,  the   bones,  the  liga- 
ments, the  veins,  the  skin,  &c.     The  great  internal  organs 
of  the  body  are  firmer,  more  fit  to  perform  their  duty,  and 
less  liable  to  disease,  if  the  circulation  in  them  is  excited 
daily  by  this  means.     Active  exercise  makes  the  stomach 
digest  better,  the  lungs  perform  the  work  of  aerating  the 
blood  more  thoroughly,  and  the  brain  serve  the  mind  more 
easily  and  effectually  ;  it  therefore  renders  one  less  liable  to 
dyspepsia,  to  consumption  and  other  diseases  of  the  lungs, 
and  to  apoplexy  and  other  diseases  of  the  brain  and  the  ner 
vous  system. 

631.  But  the  activity  of  the  circulation  may  be  made  sc 
violent  by  exercise  as  to  do  some  damage.     Though  its  or 
gans  are  capable  of  bearing  much  in  this  respect,  there  is 
some  need  of  caution.     Harm  is  undoubtedly  often  done  i» 
trials  of  strength  when  the  effort  is  both  violent  and  prolong- 
ed.   Vigorous  action  answers  fully  the  purpose  of  developing 
power  and  firmness ;  but  violent  action  is  attended  with  some 
hazard. 

632.  In  considering  the  hygiene  of  formation  and  repair, 
it  must  be  borne  in   mind  that  there  is  constant  change 
everywhere  in  the  system.     Particles   that  have   become 
useless  in  the  textures  are  continually  taken  up  and  carried 
away  in  the  veins  or  the  lymphatics,  and  other  particles  are 
put  in  their  places,  being  taken  for  this  purpose  from  the 
blood  in  the  capillaries.     This  change  is  going  on  during  all 
the  period   of  growth,  as  well  as  afterwards.     The  health 
and  vigor  of  the  textures,  and  therefore  of  the  system  as  a 
whole,  are  dependent  upon  the  proper  performance  of  this 
constant  process  of  removal  and  fresh  supply. 

633.  There  are  two  conditions  necessary  to  the  due  per- 
formance of  this  process.     The  first  Vs,  that  the  blood,  the 


HYGIENE.  897 

Necessity  of  a  free  discharge  of  the  -waste.    Functions  of  the  skin. 


universal  material  for  building  and  repairing,  shall  be  of 
good  quality.  This  is  secured  when  the  digestive  process, 
which  furnishes  the  blood,  is  well  performed,  and  the  lungs 
and  other  organs,  that  purify  the  blood  by  discharging  its 
refuse  matter,  are  in  good  condition.  The  second  condition 
is,  that  the  blood  shall  be  often  quickened  in  its  course 
through  the  organs  by  the  excitement  of  exercise.  This  I 
have  already  mentioned  in  speaking  of  the  hygiene  of  the  cir- 
culation. 

634.  The .  necessity  of  having  the  waste  matter  that  is 
brought  back  from  all  parts  of  the  body  in  the  venous  blood, 
effectually  discharged  by   the  various  organs  designed  for 
this  purpose  (§178),  requires  a  particular  notice.     The  lungs, 
the  skin,  the  liver,  the  kidneys,  &c.,  must  thoroughly  eva- 
cuate this  waste,  or  its  retention  will  impair  the  quality  of 
the   blood,  and  thus  interfere  with  the  proper  nutrition  of 
the  body,  or,  in  other  words,  with  the  process  of  formation 
and  repair.     And  the  retention  of  this  refuse  in  any  consid- 
erable amount  is  immediately  productive  of  disease. 

635.  The  lungs,  while  they  take  in  oxygen  from  the  air, 
discharge  carbonic  acid  gas,  that  part  of  the  waste  of  which 
it  is  their  duty  to  rid  the  system.     If  this  carbon  be  retain- 
ed, the  blood  is  impure  in  proportion  to  the  degree  of  reten- 
tion. 

636.  It  is  the  duty  of  the  skin  to  discharge  some  portion 
of  the  refuse  of  the  system  in  the  sensible  and  insensible 
perspiration  (§180).    The  skin   is  not  a  mere  covering  of 
the  body,  but  it  is  also  an  active  organ,  performing  very 
important  functions.     It  continually  discharges  through  its 
numberless  pores  a  large   quantity  of  matter.     Although 
this  matter  is  mostly  in  an  insensible  form,  if  from  inactivi- 
ty of  this  organ  it  fail  to  be  discharged,  its  retention  renders 
the  blood  impure,  and  so  does  injury  to  the  system.     At 
least  two  pounds  of  matter  are  discharged  from  the  skin  in 
twenty -four  hours.     This  being  the  case,  it  is  not  at  all  won- 
derful that  activity  of  this  organ  should  be  so  necessary  to 
health,  and  that  the  suspension  of  its  secretions  should  have 
so  much  influence  in  the  production  of  disease. 

637.  In  the  chapter  on  respiration,  you  learned  that  the 
heat  of  the  body  is  produced  by  the  change  that  takes  place 
in  the  blood  in  the  capillaries,  as  it  receives  the  waste  par- 
ticles, and  as  the  new  are  deposited  in  their  places.     This 
change  makes  a  real  combustion  in  every  capillary.     The 

34 


398  HUMAN   PHYSIOLOGY. 


Animal  heat.     Conditions.     Body  comfortable  only  when  giving  off  heat. 

more  rapid  therefore  is  the  change  the  greater  is  the  com- 
bustion, and  of  course,  the  greater  is  the  heat.  Hence  comes 
the  increased  heat  of  exercise.  Exercise  makes  more  wear 
and  tear,  and  so  disengages  in  the  waste  more  carbon  and 
hydrogen  to  unite  with  the  increased  amount  of  oxygen  that 
comes  in  the  quickly  flowing  blood  to  the  capillaries  ;  and 
just  as  in  combustion  that  is  attended  with  flame,  the  great- 
er the  amount  of  fuel  the  greater  is  the  heat.  We  have  a 
familiar  example  of  the  production  of  heat  by  exciting  the 
circulation,  in  the  expedient  often  resorted  to  by  laborers 
for  warming  the  hands,  of  striking  them  with  a  swinging 
motion  upon  the  shoulders. 

638.  The  amount  of  heat  produced  in  the  body  depends 
also  on  the  quality  of  the  blood.     The  richer  it  is,  the  more 
oxygen  it  contains,  and  therefore,  the  brisker  is  the  fire  in 
the  capillaries,  and  the  greater  is  the  heat.  You  see  then  why 
it  is  that  those  who  have  a  good  state  of  the  blood,  and  ex- 
ercise much,  maintain  the  heat  of  the  system  better,  and  so 
need  less  clothing  than  those  whose  blood  is  weak,  and  who 
exercise  but  little. 

639.  The  heat  of  the  body  is  maintained  in  all  temperatures 
of  the  atmosphere  very  nearly  at  98°  Fahrenheit.     This  is, 
you  observe,  much  above  even  the  highest  temperature  that 
is  agreeable  to  us.     You  see  then  that  it  is  essential  to  the 
comfort  of  the  body  that  it  be  giving  off  heat  continually  to 
the  surrounding  atmosphere.     If  the  atmosphere  be  at  98°, 
the  same  temperature  with  the  body,  there  is  great  discom- 
fort, from  the  fact  that  the  heat  is  given  off  too  slowly.     It 
would  not  be  parted  with  at  all  if  the  skin  were  not  an  ac- 
tive organ.     It  is  by  the  evaporation   of  the  perspiration 
thrown  off  by  the  skin  that  the  extra  heat  is  got  rid  of  when 
the  air  is  so  hot.     The  temperature  in  which  the  body  is 
generally  most  comfortable  is  about  70°.     When  the  atmos- 
phere goes  below  this,  we  need  the  ordinary  expedients  to 
prevent  a  too  rapid  escape  of  the  heat  from  the  body.     The 
clothing  and  the  heated   air,  with  which  we  surround  our- 
selves to  guard  against  the  cold,  do  not  act  by  communica- 
ting heat  to  the  body,  but  simply  by  retarding  its  escape. 

640.  Cold  is  a  depressing  agent,  and  exerts  as  such  much 
influence  in  the  production  of  disease.     Statistics  show  this 
in  a  striking  manner.  The  statistics  of  London,  for  example, 
prove  that  the  mortality  of  a  severe  winter  is  much  greater 
than  that  of  a  mild  one.     And  this  difference  is  found  to  be 


HYGIENE.  399 


Means  of  guarding  against  cold.    Principles  to  be  observed  in  using  them. 

chiefly  among  the  very  young  and  the  very  old,  because  in 
them  the  power  of  generating  heat  is  feebler  than  in  other 
classes.  The  greater  is  this  heat-producing  power  in  the 
system,  the  better  does  the  system  resist  the  depressing  in- 
fluence of  cold.  All  those  means,  therefore,  which  promote 
the  vigor  of  the  body,  are  the  best  of  the  safeguards  to  be  used 
against  this  productive  cause  of  disease  and  death.  But, 
besides  thus  fortifying  the  body  internally  against  this 
depressing  agent,  we  have  the  means  of  outer  defence  alluded 
to  in  §  639,  clothing  and  heated  air.  As  there  are  many 
errors  committed  in  using  these,  they  require  a  more  parti- 
cular notice. 

641.  Clothing  serves,  as  I  have  before  said,  to  shut  in 
partially   the  heat  which  is  generated   in   the   body.      Its 
amount  and  character  should  be  regulated  by  two  circum- 
stances— the  degree  of  the  cold,  and  the  amount  of  heat-gen- 
erating power  in  the  system.     The  vigorous   require   less 
clothing  than  the  weak,  because  they  have  more  of  this  power; 
so,  also,  the  body  needs   less  clothing  when  it  is  in  exercise 
than  when  it  is  in  a  state  of  rest,  because  in  exercise  it  gene- 
rates more  heat.     And  the  same   principles  apply  to  heated 
air,  for  this   is  an  outer  covering  for  the  body,  interposed 
between  it  and  the  cold,  like  clothing,  for  the  purpose  of 
preventing   the   too   rapid    escape   of   the   heat    generated 
within. 

642.  These  plain  principles  are  violated  in  various  ways. 
Many,  from  carelessness  or  from  mistaken  notions,  are  often 
unnecessarily  exposed  to  the  depressing  influence  of  cold. 
They  are  not  sufficiently  aware  of  the  necessity  of  guarding 
so  much  more  thoroughly  against  the  cold  when  at  rent  than 
when  exercising.     And  then,  on  the  other  hand,  they  add  to 
the  effect  by  having  too  much  clothing  when  in  action,  or  when 
in  a   warm  place.     When  they  thus   suffer  first  from   too 
much  heat,  an  after  exposure  to  cold   is  exceedingly  inju- 
rious.    The  weak   especially  suffer  from  exposure  to  cold 
when  the  body  is  at  rest,  and  therefore,  they  should  take 
special  pains  to  guard  themselves  against  this   depressing 
agent.  Any  attempt  on  their  part  to  harden  themselves,  as  it 
is  expressed,  by  making  use  of  as  little  clothing  as  the  vigor- 
ous wear,  particularly  when  the  body  is  in  a  state  of  inaction, 
always  does  harm.     The  very  thin  coverings  so  commonly 
seen  on  the  feet  of  delicate  females  are  palpably  inconsistent 
with  this  rule  of  hygiene,  and  are  in  ridiculous  contrast  with 


400  HUMAN  PHYSIOLOGY. 

Cold  sometimes  a  stimulant.     Conditions  on  which  reaction  depends. 


the  stout  coverings  considered  necessary  for  the  feet  of 
rigorous  men.  Various  opinions  have  been  expressed  in 
regard  to  the  warming  of  houses,  so  much  in  vogue  at  the 
present  day.  On  the  principles  developed  above,  this  ex- 
pedient for  comfort  is  favorable  to  health  if  it  be  judiciously 
managed,  for  when  the  body  is  at  rest,  as  it  commonly  is  in- 
doors, an  exposure  to  cold  is  depressing,  that  is  debilitating 
to  the  vital  powers.  Many  other  points  might  be  noticed 
in  the  application  of  the  general  principles  mentioned,  but 
these  will  suffice. 

643.  The  depressing  influence  of  cold  sometimes  produces 
a  marked  immediate  effect.     But  this  is  not  generally  the 
case.     Commonly  no  harm  is  apparently  done  at  the  time, 
and  so  little  is  thought  of  it.     But  if  this  influence  be  con- 
tinued day  after  day,  its  effects  accumulate  and  become  estab- 
lished.    The  vigor  of  the  system  is  more  or  less  destroyed, 
and  some  local  disease  may   make  its   appearance.      The 
debilitating  influence  of  cold  is  in  this  way  a  fruitful  cause 
of  disease,  not  only  in  the  abodes  of  poverty,  but   even 
among  those  who  have  ample  means  of  guarding  against  it. 

644.  Although  cold  is  generally  a  depressing  agent,  it  is 
often  indirectly  a  stimulating  one.     It  is  so  when,  in  conse- 
quence of  its  impression  upon  the  skin,  it  excites  what  is 
termed  a  reaction.     Several  circumstances  are  necessary  to 
this  result.     1.  There  must  be  the  power  of  reaction  in  the 
system.     There  may  be  so  much  debility  that  reaction  can- 
not be  awakened.    2.  If  the  system  be  in  a  state  of  rest,  the 
application  of  cold  must   be   temporary.      A   continuous 
application  of  it  would  be  depressing,  and  would  forbid  reac- 
tion.   3.  In  an  active  state  of  the  body,  reaction  may  be  pro- 
duced even  when  the  application  is  continuous.      Thus  the 
mere  exercise  of  dressing  may  suffice  to  awaken  reaction  in 
a  degree  of  temperature  which  would  chill  one  through  if  he 
were  sitting  still. 

645.  The  system  may  be  accustomed  to  react  under  the 
impression  of  cold   in  two   ways.     1.  By  exercise  in   the 
open  air  in  cold  weather.     Those  who  have  but  little  out- 
door exercise  in  cold  weather,  have  but  little  power  of  re- 
action, and  therefore  feel  the  depressing  influence  of  the  cold 
whenever  they  are  exposed  to  it.     2.     By  a  judicious  use 
of  cold   bathing.     The   object  of  cold  bathing,  aside  from 
purposes  of  cleanliness,  is  to  accustom  the  system  to  react 
under  the  influence  of  cold.     It  is  only  when  reaction  occurs 


HYGIENE.  401 


Cold  bathing.     To  be  used  variously  in  different  cases. 


under  its  use  that  it  does  good.  It  does  positive  harm  when 
reaction  does  not  occur ;  and  the  harm  done  in  this  way 
day  after  day,  by  depressing  the  vital  powers,  is  sometimes 
at  length  ruinous  to  the  health. 

646.  There  is  a  want  of  proper  discrimination  in  many 
writers  on  hygiene  in  regard  to  cold  bathing.     It  is  a  mis- 
taken ultraism  to  say,  as  is   often   said,  that  the  preserva- 
tion of  health  requires  that  the  whole  body  should  be  bathed 
every  day  in  cold  water.     Neither  cleanliness  nor  the  other 
purpose  that  I  have  mentioned  ordinarily  requires  so  frequent 
and  thorough  bathing  as  this.     The  water  may  be  applied 
to  only  a  part  of  the  body  at  a  time,  and  yet  accomplish  all 
that  we  wish.     Indeed,  some  persons  of  delicate  constitution 
cannot  bathe   the  whole  surface  at  once  with  cold  water. 
They  may  at  first  be  able  to  apply  it  to  only  a  small  part  of 
the  body.     But  they  may,  with  the  aid  of  friction,  after  a 
while  come  to  apply  it  over  a  considerable  portion  of  the 
surface,  or  perhaps  over  the  whole.     In  some  persons  this 
extension  of  the  limits  of  the  bathing  from  day  to  day  must 
be  done  very  cautiously  ;  and  there  is  occasionally  one  that 
cannot  bear  it  at  ail  over  any  considerable  extent  of  surface. 
It  is  necessary  for  some,  in  accustoming  themselves  to  cold 
bathing,   to  begin  with  using  tepid  water,   making  it  from 
day  to  day  a  little  colder. 

647.  The  best  time  for  cold  bathing  is  commonly  in  the 
latter  part  of  the  forenoon,   for  the  system  is  then  in  its 
most  vigorous  state,  and  is  therefore  best  prepared  to  re- 
act.    But  in  most  persons  reaction  can  be  secured  at  the 
hour  of  rising,  and   this  is  the  most  convenient  time  for 
bathing.     Few  can  use  the  cold  bath  with  profit  in  the  latter 
part  of  the  day,  for  the  powers  of  the  system  are  then  more 
or  less  exhausted,  and  full  reaction  is  not  easy.     The  sooth- 
ing influence  of  the  warm  bath  is  appropriate  at  that  time. 
There  are  many  other  points  in  regard  to  bathing  that  might 
be  noticed,  but  my  limits  will  not  permit  it. 

648.  Thus  far  I  have  spoken  mostly  of  the  hygiene  of  the 
body  as  a  structure.     But  digestion,  the  circulation,  &c,  are 
engaged  in  constructing  and  repairing  organs  for  the  use  of 
the  mind.     In  this  use,  there  is  wear  and  tear,  and  hence  is 
the  necessity  of  seasons  of  rest,  that  the  needed  daily  repaif 
of  the  organs  may  be  effectually  done.     The  mind  uses  the 
muscles  and  bones  for  motion,  the  various  organs  of  the 
senses  in  gaining  a  knowledge  of  the  world  around,  and  the 

34* 


402  HUMAN  PHYSIOLOGY. 

Exercise  necessary  to  the  development  of  both  the  muscles  and  the  other  organs. 

brain  in  thinking,  willing  and  designing.  Any  of  these 
organs  may  be  overworked,  and  after  a  certain  amount  of 
work  has  been  done,  there  needs  to  be  an  interval  of  rest 
for  repair.  The  repair  is  going  on  continually,  while  the 
organs  are  at  work  ;  but  it  cannot  be  done  thoroughly  with- 
out these  intervals  of  rest.  Most  of  the  repairing  is  done 
in  these  periods.  This  simple  statement  suggests  the  prin- 
ciples of  hygiene  in  regard  to  the  uses  which  the  mind 
makes  of  the  organs  of  the  body.  These  I  propose  now  to 
develop  briefly  in  regard  to  the  muscles,  the  senses,  and 
lastly  the  brain. 

649.  There  is   a   certain   amount   of  muscular   exercise 
which  is  essential   to  firm   health.     While  no  one  can  fall 
below  this  amount  without  impairing  the  healthy  vigor,  the 
laborer  goes  much  beyond  it  without  injury.     There  is  a 
wide  range,  therefore,  in  the  amounts  of  muscular  exertion 
that  are  consistent  with  health. 

650.  The  exercise  of  the  muscles  is  necessary  to  their  full 
development.     When  a  limb  fails  to  be  used,  as  for  exam- 
ple in  palsy,  the  muscles  become  small  and  lose  their  firmness. 
When,  on  the  other  hand,  the  muscles  of  any  part  of  the 
body  are  much  used,  they  become  more  developed  than  the 
other  muscles.     For  example,  the  labor  of  the  blacksmith 
develops  the  muscles  of  his  arms  largely.     The  same  thing 
is  true  of  the  muscles  of  the  leg  in  the  rope-dancer.     It  is 
only  a  general  exercise  of  all  the  muscles  of  the  body  that 
develops  them  in  all  parts  of  the  frame  in  their  due  propor- 
tion. 

651.  But  muscular  exercise  is  also  necessary  to  the  pro- 
per development  of  the  other  textures  as  well  as  the  muscles. 
I  have  already  remarked  upon   this  in  another  connection 
(§  630),  and  shall  not  dwell  upon  it  here.  There  is,  however, 
one  illustration  of  this  influence  of  exercise  which  deserves  a 
particular  notice.     I  refer  to  its  influence  in  preventing  de- 
formity.   In  the  universal  vigor  and  firmness  of  the  textures 
which  free  exercise  tends  to  produce,  there  is  ordinarily  a 
precise  equality  between  the  two  halves  of  the  body  :  the 
muscles  on  the  two  sides  act  with  equal  power;  the  spinal 
column,  the  grand  pillar  of  the  trunk,  is  held  between  the 
muscles  that  bind  its  twenty-four  bones  together  with  great 
exactness,  and  there  is  a  beautiful  symmetry  in  the  whole 
frame.     But  when,  from  lack  of  exercise,  there  is  want  of 
firmness   in  the  textures,  this  symmetry  is  apt  to  be  lost 


HYGIENE.  403 


Deformity  of  the  spine — why  more  common  in  females  than  males. 

during  the  development  of  the  frame,  and  the  spinal  column 
is  especially  apt  to  become  deformed. 

652.  There  are  two  immediate  causes  of  this  deformity, 
viz. : — irregular  muscular   action,   and    irregular   pressure. 
Weakened  muscles  are  prone  to  act  irregularly  ;  and  struc- 
tures that  have  lost  their  firmness,  readily  yield  to  any 
pressure  that  is  laid  upon  them.     When  there  is  firmness  of 
texture,  irregularities  of  pressure  are  not  apt  to  produce  de- 
formity, because  the  elasticity  prevents  the  permanent  in- 
fluence of  such  pressure.     The  moment  the  pressure  ceases, 
the  elasticity  of  the  part  restores  it  to  its  usual  shape.    The 
firm  regular  action  of  the  muscles  also  tends  to  the  same 
result.      Thus,   in    the   case  of  the   spinal   column,   if  the 
posture  of  the  body  be  such  that  it  is  bent  over  to  one  side 
for  some  time,  the  moment  that  the  posture  is  altered,  the 
elastic  cartilages   resu«me  their  usual  shape  which  has  been 
temporarily  changed  by  the  unusual  pressure,  and  the  mus- 
cles also  that  lie  along  this  pillar  of  bones  bring  them  at 
once  to  their  right  position.     But  if  the  cartilages  have  lost 
in  some  measure  their  elasticity  and  the  muscles  are  weak, 
this  righting  up  of  the  spinal  column  is  not  fully  accomplish- 
ed ;  and  a  succession  of  slight  failures  in  this  respect  will 
after  awhile,  produce  a  permanent  deformity  in  the  direction 
of  the  most  commonly  assumed  posture. 

653.  You  can  see  all  this  exemplified  if  you  observe  the 
difference  between  males  and  females  in  regard  to  deformity 
of  the  spine.    This  deformity  is  exceedingly  common  among 
girls,  while  it  is  rare  among  lads.  The  simple  reason  is,  that 
lads  have  the  invigorating  influence  of  free  out-door  exercise. 
Too  much  influence  is  attributed  to  posture  in  producing  this 
deformity.     Posture  is  often  spoken  of  as  being  the  chief 
cause  of  it,  and  this  view  of  the  subject  is  illustrated  exten- 
sively with  cuts,  showing  how  the  deformity  is-  occasioned.  If 
this  were  the  correct  view,  there  should  be  much  less  deform- 
ity among  girls  than  among  boys  in  our  schools,  for  the  form- 
er sit  in  a  crooked  posture  much  less  than  the  latter  do. 
So  far  as  posture  does  have  an  influence,  it  is  quite  clear  that 
the  prim,  fixed  posture  enjoined  upon  the  girl  has  a  tendency 
to  produce  deformity,  by  adding  to  one  of  the  causes  from 
which  it  proceeds,  viz.,  the  weakness  of  the  muscles.  A  fixed 
uniform  posture  wearies  the  muscles,  but  variations  of  posture 
relieve  them,  and  so  prevent  an  exhaustion  of  their  power. 

654.  The  muscles  of  the  back  in  the  female  are  not  only 


404  HUMAN  PHYSIOLOGY. 

Exercise  should  be  varied  and  general.     Gymnastics  and  Calisthenics. 

weakened  in  common  with  the  other  muscles  by  a  want  of 
stirring  out-door  exercise,  but  there  is  a  special  cause  of 
weakness  in  their  case.  The  tight  dress  of  the  girl  prevents 
these  muscles  from  having  that  free  action  which  the  loose 
dress  of  the  boy  permits.  You  can  see  this  in  the  difference 
of  movement  in  the  two  cases.  In  the  boy,  the  spine  is  bent 
and  twisted  in  all  directions  freely  ;  but  in  the  girl,  both 
custom  and  the  stiff  tightness  of  the  dress  require  a  move- 
ment almost  as  if  the  spine  were  a  single  bone,  instead  of 
being  made  up  of  twenty-four  bones.  The  muscles  in  her 
back,  therefore,  lose  their  power  and  fulness  just  as  the  un- 
used muscles  of  a  palsied  limb  do. 

655.  Variety  should  be  aimed  at  in  the  action  of  the  mus- 
cles.    A  continuous  action  of  any  set  of  muscles  is  weari- 
some and  painful.     This  is  well  exemplified  in  the  punish- 
ment  once  much  in   vogue  in  schools,   of  making   the  of- 
fender hold  a  book  out  at  arm's  length  for  some  time.     In 
the  management  of  the  muscles  of  the  voice,  the  weariness 
caused  by  continued  sameness  of  action  is  often  experienced. 
The  monotonous  speaker  or  reader  tires  out  these  muscles 
much  sooner  than  one  who  has  great  variety  in  his  tones. 
For  remarks  on  this  and  some  other  kindred  points,  I  refer 
you  to  §§  382  and  383. 

656.  A  general  exercise  of  all  the  muscles  is  essential 
both  to  symmetrical  muscular  development,  and  to  the  full 
attainment  of  the  invigorating  effects  of  exercise.     Gymnas- 
tics and  calisthenics,  so  called,  are  considered   to  be  particu- 
larly beneficial  in  this  respect.     This  is  true  of  them ;  and 
yet  they  are  no  better  than  any  other  exercises  that  are  so 
varied  as  to  bring  the  muscles  generally  into  action.     The 
varied  exercises  of  walking,  running,  leaping,  riding  on  horse- 
back, dancing,.and  active  sports,  are  quite  as  good.     And  so 
also  are  the  varied  labors  of  the  garden,  if  they  be  pursued 
with  interest   and  pleasure.     There  is  no  especial  benefit 
in  the  extreme  variety  of  exercise  sometimes  aimed  at  in 
gymnastics.     Variety  that  is  sufficient  to  bring  into  general 
action  the  muscles  of  the  body  is  all  that  is  requisite. 

657.  Gymnastics  and  calisthenics  should   always  be  con- 
sidered as  subsidiary  to  the  common  exercises  that  I  have 
mentioned,  and  should  never  be  permitted  to  exclude  them. 
When  they  are  made  to  do  this,  a  temporary  benefit  is  reap- 
ed at  the  expense  of  a  permanent  injury.     For  after  the 
novelty  of  the  round  of  exercises  has  passed  away,  they 


HYGIENE.  405 


Effect  of  too  severe  exercise.    Hygiene  of  the  Senses. 


are  given  up,  and  the  common  and  now  despised  exercises 
are  not  apt  to  be  resumed.  Habits  of  inaction,  therefore,  are 
often  confirmed,  instead  of  being  removed,  by  a  systematic 
course  of  exercises  under  the  high-sounding  names  of  gym 
nasties  and  calisthenics. 

658.  It  is  necessary  that  some  of  the  exercise  taken  should 
be  such  as  to  excite  strongly  the  circulation.     This  I  have 
already  remarked  upon.      Exercise  should  also  be   taken 
daily.     It  should  be  habitual,  and  not  occasional.    The  habits 
of  the  English  are  much  better  than  those  of  the  Americans 
in  this  respect.     It  is  no  uncommon  thing  for  English  ladies 
to  walk   off  on   excursions   of  such  length,   that  American 
ladies  could  not  possibly  accompany  them  unless  they  rode. 

659.  But  there  may  be  too  much  exercise.     The  toil  of 
the  laborer  may  be  so  severe  and  long  continued,  that  the 
reparative  process  in  the  intervals  of  rest  is  not  competent 
to  effect  a  full  repair  of  the  muscles.     A  gradual  exhaustion 
of  their  power  therefore  results.    Much  harm  is  thus  often 
done  by  severe  unremitting   toil.     Especially   is  this  the 
case  when  the  excess  of  toil  is  exacted  during  the  period  of 
growth,  as  it  often  is  among  the  laboring  poor. 

660.  It  is  necessary  that  exercise  should  be  agreeable  in 
order  to  produce  its  best  effect  on  the  system,  on  account  of 
the  genial  excitement  which  then  accompanies  it.     For  this 
reason  exercise  should  commonly  not  be  solitary,  and  there 
should,  if  possible,  be  some  object  connected  with  it.     If  the 
observation  of  nature  were  made  from  the  beginning  of  edu- 
cation as  prominent  as  I  claim  in  my  Preface  that  it  should 
be,   there  would  be  no  lack  of  objects  in  the  rambles  in 
field  and  forest  taken  both  for  health  and  the  pursuit  of 
science. 

061.  What  has  been  said  of  the  muscles  may  be  substan- 
tially said  of  the  organs  of  the  senses.  They  require  inter- 
vals of  rest  for  thorough  repair.  And  they  may  be  so  over- 
worked that  complete  reparation  may  be  impossible,  and  so 
their  power  may  be  gradually  exhausted.  The  office  of  the 
senses  is  to  receive  impressions  from  things  around.  What- 
ever gives  an  impression  to  any  organ  of  sense  may  be  re- 
garded as  a  stimulus  to  it.  If  the  stimulus  be  too  great 
or  too  long  continued,  injury  is  done.  This  is  very  obvious 
in  regard  to  the  eyes.  They  are  often  injured  by  too  much 
light.  A  word  of  caution  is  needed  in  regard  to  the  produc- 
tion of  near-sightedness.  This  is  often  caused  in  students 
and  others  by  holding  objects  too  near  the  eyes. 


406  HUMAN  PHYSIOLOGY. 

Necessity  of  seasons  of  rest  to  the  brain.      Overworking  the  brain. 

662.  I  come  now  to  the  hygiene  of  the  brain.     This  is  the 
great  central  organ  or  instrument  of  the  mind,  by  which  it 
receives  the  impressions  made  upon  the  senses,  compares 
and  arranges  the  knowledge  thus  gathered,  and  originates 
those   impressions  that  are  made   by  it   upon   the   world 
around  through  the  action  of  muscles.     It  is  a  very  com- 
pound instrument.     It  needs,  like  the  muscles,  seasons  of 
rest  for  the  full  repair  of  the  wear  and  tear  occasioned  in  its 
daily  use.     It  may  be  overworked,  and  then  the  repair  will 
not  be  complete,  and  gradual  exhaustion  of  its  powers  will 
result,  occasioning  disease  in  some  form.    A  significant  illus- 
tration of  the  importance  of  seasons  of  rest  for  repair  in  the 
case  of  the  brain  is  furnished  in  the  fact,  that  insanity  is  not 
apt  to  result  from  mental  disturbance,  unless  the  subject  of 
it  fail  to  have  his  regular  sleep.    If  he  sleeps  well,  the  work 
of  repair  is  so  well  done  in  the  brain  in  its  nightly  seasons 
of  rest,  that  the  disease,  which  might  otherwise  occur,  is 
prevented. 

663.  With  proper  intervals  of  rest,  the  mind  can  perform 
a  large  amount  of  labor  without  injury  to  the  brain  and  ner- 
vous system,  if  there  be  no  undue  excitement,  and  no  wor- 
rying and  depressing  anxiety.     This  is  shown  in  the  length 
of  life   that  so  often  accompanies  the  quiet  but  laborious 
pursuits  of  science.     While,  on  the  other  hand,  the  excite- 
ment and  anxiety  of  a  life  of  business,  especially  as  it  is 
ordinarily  pursued  in  this  country,  it  is  well  known,  is  not 
favorable  to  longevity. 

664.  It  is  especially  important  that  the  brain  should  not 
be  overworked  during  the  period  of  its  growth.     The  reason 
is  the  same  as  that  which  we  have  for  the  caution,  so  univer- 
sally observed,  in  regard  to  putting  too  much  labor  upon 
the  muscles  of  a  young  horse.     And  yet  there  is  buoyant 
activity  in  the  child,  which  is  disposed  to  show  itself  in  the 
operations  of  the  brain  as  readily  as  in  the  action  of  the 
muscles.     If  this  activity  be  turned  into  proper  channels, 
and  be  not  too  much  stimulated,  no  injury  will  be  done  to 
the  delicate  textures  of  the  brain. 

665.  Although  much  is  said  of  the  danger  of  over-stimu- 
lating the  brain  of  the  child,  the  difficulty  does  not  so  much 
lie  here,  as  in  the  manner  in  which  the  mind  is  led  to  act. 
There  is  commonly   too  much  of  mere  drudgery,  and  of 
storing  the  mind  with  unintelligible,  and  therefore  uninter- 
esting matters.     The  mind,  accordingly,  is  dissatisfied  and 


HYGIENE.      v  407 


Influence  of  quiet  cheerfulness.     The  passions.    Alcoholic  stimulants. 

wearied.  The  tedium  of  the  labor  exhausts,  and  so  the 
brain  is  essentially  impaired.  When  early  education  shall 
become  in  all  respects  what  it  ought  to  be,  greater  real  ac- 
quisitions will  be  made  than  we  witness  now,  without  any 
injury  to  the  growing  brain. 

666.  It  is  well  known  that  undue  mental  excitement  and 
the  depression  of  anxiety  are  together  apt  to  produce  insanity. 
Though  they  generally  stop  short  of  this  result,  they  always 
injure  the  health  and  shorten  life.     A  firm  and  cheerful  mind 
is  favorable  to   longevity,  but  the  anxious  and  fretting  are 
seldom,  if  ever,  long-lived. 

667.  As  the  passions  must  have  much  influence  upon  the 
action  of  the  mind,  and  therefore  upon  the  state  of  the  brain 
and  nervous  system,  the  proper  regulation  of  them  is  essen- 
tial to  health  and  longevity.     Much  of  the  positive  disease 
of  the  brain,  and  of  the  general  nervous  derangement  so 
common  among  the  educated  and  refined,  comes  from  the 
bad  management  of  the  passions.     I  cannot  dwell  upon  this 
point,  but  remark,  in  passing,  that  the  fictitious  literature 
of  the  present  day  exerts  a  considerable  influence  in  this 
way. 

668.  There  are  certain  articles  in  common   use  in  the 
community,  which  produce  so  deleterious  an  influence  upon 
the  system,  that  they  demand  a  more  extended  notice  than  I 
can   give   them   in  this   chapter.     I    refer   to   alcohol    and 
tobacco.       They   act  chiefly  upon  the  brain    and   nervous 
system,  the  former  as  a  stimulant,  and  the  latter  as  a  seda- 
tive.    The  use  of  opium  is  so  limited  compared  with  these 
that  I  shall  not  dwell  upon  it,  especially  as  it  is  never  de- 
fended. 

669.  No  fact  is  more  thoroughly  demonstrated  than  that 
the  system  has  no  need  of  alcoholic  slimulants  while  it  is  in 
a  state  of  health.     So  far  then  as  we  look  at  mere  necessity, 
these  articles  are  to  be  considered  simply  as  medicines,  re- 
quired only  in  diseased  conditions.     But  it  is  said  by  some 
that  they  can  be  used  in  small  quantities  without  injury  to 
health.     This  cannot  be  claimed  with  any  shadow  of  reason, 
unless  in   relation  to  very  small  quantities.     Entire  absti- 
nence is  at  least  safe,  and  there  are  so  many  other  things 
supplied  by  a  bounteous  Providence  to  gratify  the  taste  and 
the  appetite,  that  we  can  easily  forego  the  use  of  alcoholic 
stimulants;  and  we  ought  to  be  willing  to  do  so,  if  the  good 
of  others  require  it.     The  common  use  of  these  articles  as 


408  HUMAN   PHYSIOLOGY. 

Tobacco  an  active  poison.      Coffee  and  Tea — the  propriety  of  their  use  not  settled. 

beverages  is  one  of  the  most  prolific  of  the  sources  of  disease  ; 
and  it  is  a  significant  fact,  that  the  very  moderate  use,  claim- 
ed by  some  to  be  innocuous,  has  a  strong  tendency  to  pass 
into  a  larger  use,  even  so  large  that,  its  deleterious  influence 
upon  health  is  palpable. 

670.  The  evidence  is  quite  as  clear  in  relation  to  the  inju- 
rious effects  of  tobacco.  This  has  sometimes  been  erroneous- 
ly termed  a  stimulant.     The  error   arises   from   the  well- 
known  discomfort  of  the  habitual  user  of  it  when  he  is  depri 
ved  of  the  use  of  this  drug.     This  discomfort  has  a  depress- 
ing influence,  and  when  his  system  is  brought  again  under 
the  influence  of  tobacco  the  depression  is  removed,  not  by 
any  direct  stimulating  effect,  but  by  the  relief  given  to  the 
uncomfortable   sensations.     Tobacco  is   really    one   of  the 
purest  sedatives  we  have.     It  depresses  vital  action.    It  acts 
chiefly  upon  the  nervous  system,  and  therefore,  has  a  strong 
tendency  to  produce  nervous  diseases.     While  it  is  injurious 
to  all,  it  is  especially  so  to  those  who  have  a  low  vital  action, 
and  are  disposed  to  nervous  complaints. 

671.  Tobacco  is  so  active  a  poison  that  extreme  caution 
is  required  whenever  it  is  administered,  as  it  sometimes  is, 
as  a  medicine.    The  effects  of  even  a  small  amount  of  it  upon 
one  that  is  unaccustomed  to  its  use  are  of  the  most  decisive 
character.     And  that  must  be  an  exceedingly  artificial  con- 
dition of  the  system,  in  which,  by  continued  use  of  this  drug, 
large  amounts  come  to  be  borne  with  little  apparent  effect. 
The  evidence  of  the  deleterious  influence  of  tobacco  upon  the 
system  is  as  unequivocal  as  that  which  we  have  in  regard  to 
the  influence  of  opium,  and  wonderfully  strong  is  that  sla- 
very to  appetite  that  makes  one  persist  in  the  use  of  this  drug 
in  spite  of  such  evidence. 

672.  Coffee  and  tea  are  often  included  in  the  same  cate- 
gory with  alcohol  and  tobacco.     Granting  all  that  is  claimed 
in  regard  to  the  injurious  effects  of  these  articles,  it  is  pre- 
posterous to  class  them  with  such  poisons.     The  evidence  in 
regard  to  them  is  conflicting,  and  all  that  is  settled  as  yet  is, 
that  in  some  persons  they  exert  a  bad  influence  upon  the 
nervous  system.     If  this  should  be  found  to  be  true  of  a 
very  large  proportion  of  all  who  use  them,   the  evidence 
would  be  conclusive  against  the  propriety  of  their  use  as 
common  beverages.     But  as  yet  this  has  by  no  means  been 
proved  to  be  true. 

673.  There  are  certain  coisonous  emanations,  to  which 


HYGIENE.  409 


Poisonous  emanations.     General  view  of  the  causes  of  disease. 


the  human  system  is  often  subjected,  that  are  largely  de- 
structive  of  health  and  life.  They  arise  from  decomposing 
filth  of  various  kinds.  Besides  predisposing  the  system  to 
the  action  of  contagious  and  epidemic  causes  of  disease,  they 
also  of  themselves  create  disease.  It  is  these  emanations 
that  render  the  close  air  of  a  crowded  city,  especially  in  its 
narrow  lanes,  so  impure  and  fairly  poisonous.  And  this 
impurity  of  the  air  is  one  of  the  chief  causes  of  the  difference 
in  disease  and  mortality  between  the  city  and  the  country. 
The  difference  is  greater  than  is  generally  supposed.  It  has 
been  found  by  statistics  in  England,  that  there  are  24  per 
cent,  more  deaths  from  consumption,  and  55  per  cent,  more 
deaths  from  typhus,  in  cities  than  in  the  rural  districts,  and 
the  mortality  from  the  diseases  of  childhood  is  twice  as  great 
in  the  city  as  in  the  country.  In  what  way  these  emanations 
act  we  know  not.  But,  although  much  is  to  be  attributed, 
to  a  mere  want  of  ventilation,  that  is,  to  a  lack  of  oxygen, 
there  is  no  question  that  these  emanation?  often  act  as  posi- 
tive poisons  to  the  system. 

674.  In   developing   the   principles  of  hygiene,    I    have 
noticed  many  of  the  prominent  causes  of  ili  health  and  dis- 
ease.    They  are  chiefly  these:  1.  A   disregard  in  various 
ways  of  the  rules  relating  to  the  digestive  process.     2.  Com- 
pression of  the  chest,  especially  during  the  period  of  growth. 
3.  Deficiency  in  the  supply  of  pure  air  to  the  lungs.    4.  Fail- 
ure  to   guard  properly    against  the  influence  of  cold  and 
heat,  chiefly  the  former.     5.  A  lack  of  active  exercise  in  the 
open   air.     6.  Overworking  the  muscles.     7.  Errors  in  the 
management  of  the  moral  and  intellectual  powers.     8.  The 
influence  of  such  articles  as  alcohol  and  tobacco.    9.  Emana- 
tions from  decomposing  filth.     It  is  well    thus  to  look  at 
these  causes  grouped  together,  endeavoring  to  give  to  each 
its  due  prominence.     For  various  and  exclusive  views  are 
often  taken  of  this  subject.     Quite  commonly  some  of  these 
causes  are  kept  entirely  out  of  view,  while  others  are  strong- 
ly pressed  upon  our  attention.     Disease  is  generally  a  very 
compound  remit,  produced  by  a  concurrence  of  several  of 
these  causes,  and  sometimes  even  of  all  of  them. 

675.  These  causes  of  disease,  it  will  be  observed,  are  more 
or  less  under  our  control.     Some  of  them  are  entirely  so. 
A  knowledge  of  their  operation,  and  an  earnest  endeavor  to 
remove  them,  would,  therefore,  vastly  diminish  the  amount 
of  ill  health  and  disease. 

35 


410  HUMAN   PHYSIOLOGY. 

Our  control  over  the  causes  of  disease.     Preventive  and  curative  measures. 


676.  It  is  true  that  there  are  some  other  causes  of  disease, 
of  which  we  know  but  little,  and  over  which  we  have  little  or 
no  control.     Such  are  the  causes  of  various  contagious  and 
epidemic  diseases.     But  these  really  produce  a  much  less 
amount  of  disease  than  the  causes  which  I  have  mentioned. 
Their  action  is  occasional,  and  confined  to  localities  ;  not 
continual,  and  in   all  places.     And  besides,  they  may  to  a 
great  extent  be  shorn  of  their  power,  by  guarding  against 
those   causes  of  disease  which  are  more  or  less  under  our 
control.     It  is  tho?e  who  neglect  to  do  this  that  commonly 
become  most  readily  the  victims  of  contagions  and  epide- 
mics. 

677.  There  is  much  interest  in  the  community  in  regard 
to  the  cure  of  disease,  but  there  is  a  blind  indifference  to  its 
prevention.     And  yet  vastly  more  can  be  done  in  the  diminu- 
tion of  disease  by  preventive  than  by  curative  measures.     The 
ravages  of  consumption,  for  example,  can  undoubtedly  be 
greatly  lessened  by  preventing  the  operation  of  its  principal 
causes  ;  and  yet  what  is  said  about  these  causes  is   little 
heeded,    and    the   public    attention    is   engrossed  with   the 
delusions   of  consumption-curers.      It  is  emphatically  true 
of  this   malady,    that  multitudes  more  can   be  saved    by 
preventive   measures  than  by  curative  ones.     Against   no 
disease   can   hygiene  achieve   greater   victories   than   this. 
The  neglect  to   use  preventive  measures  against  this  and 
other  diseases  arises  chiefly  from  an  ignorance  of  the  prin- 
ciples on  which  these  measures  are  based.     The  prevalent 
indifference,  therefore,  on  this  subject  can  never  be  fully  re- 
moved, till  the  general  introduction  of  Physiology  as  a  study 
into  our  schools  shall  make  these  principles  familiar  to  the 
mass  of  the  community. 


APPENDIX : 


CONTAINING 


DIRECTIONS  TO  TEACHERS  FOR  THE  USE  OF  THE  BOOK, 
AND  QUESTIONS. 


IN  order  to  be  able  to  teach  from  this  book  properly,  the  teacher  should 
himself  study  all  of  it  thoroughly  before  he  begins  his  instruction.  If 
he  merely  keep  a  little  in  advance  of  his  class,  he  will  fail  in  his  concep- 
tions of  the  general  scope  and  plan  of  the  book.  If  the  interest  of  the 
subject  awaken  in  him  and  in  his  pupils  a  spirit  of  inquiry,  there  will 
be  a  continual  looking  forward  to  points  which  are  explained  and  illus- 
trated further  on  in  the  book.  Now  if  the  teacher  has  made  himself 
master  of  all  the  subjects  treated  of,  instead  of  turning  off  the  inquiry 
of  a  scholar  without  an  answer,  or  even  the  promise  of  an  answer  in  the 
future,  or  endeavoring  to  clear  up  the  points  about  which  inquiry  is 
made,  which  of  course  he  can  do,  under  the  circumstances,  in  an  imper- 
fect manner  at  the  best,  he  can  satisfy  the  scholar  by  informing  him  that 
these  points  will  be  found  explained  in  their  proper  place  at  a  future 
stage  of  the  investigation.  I  have  aimed  to  have  every  topic  treated  of 
in  its  right  place  in  the  development  of  the  general  subject,  and  the 
teacher  should  be  thoroughly  master  of  the  whole  book  at  the  outset,  in 
order  that  he  may  fully  carry  out  my  plan  in  the  mode  of  developing  the 
topics  to  the  minds  of  his  pupils. 

It  must  be  obvious  to  any  teacher  that  he  can  teach  the  minutiae  of 
the  subject  with  more  of  interest,  to  say  nothing  of  thoroughness,  if, 
while  doing  it,  he  takes  in  the  general  views  presented,  and  has  in  mind 
the  relations  of  the  particular  topics  in  hand  to  other  branches  of  the 
subject.  Indeed  it  will  be  profitable  occasionally  for  the  teacher  to 
afford  the  scholar  some  glimpses  of  the  interesting  fields  to  be  explored 
further  on,  taking  care,  however,  not  to  anticipate  so  much,  as  to  mar  the 
natural  method  and  order  of  developing  the  whole  subject,  which  I  have 
taken  such  especial  care  to  observe  in  the  preparation  of  the  work. 

The  teacher  should  read  the  book  through  in  course.  If,  instead  of 
doing  this,  he  opens  to  some  chapter  in  the  middle  or  latter  part  of  the 
book,  he  may  get  the  impression  that  too  high  matters  are  treated  of, 
and  that  the  minds  of  his  pupils  are  not  competent  to  understand  them. 
They  cannot  be  understood  unless  there  be  a  preparation  of  mind  for 
them  ;  and  just  this  preparation  is  aimed  at  ii;  the  first  part  of  the 
book.  And  besides,  ii  is  quite  important  that  the  subjects  treated  of 


412  APPENDIX. 


should  be  developed  to  the  mind  of  the  teacher  in  the  same  order  m 
which  they  are  to  be  developed  to  the  minds  of  his  pupils. 

In  the  engravings  clearness  has  been  aimed  at  rather  than  beauty. 
Yet  I  should  not  do  the  engraver  justice  if  I  did  not  say,  that  in  beauty 
they  are  generally  quite  equal  to  those  which  we  find  in  our  standard 
professional  works  on  physiology.  It  is  to  be  borne  in  mind  that  wood- 
cuts cannot  represent  correctly  the  beauty  and  delicacy  of  living  struc- 
tures. These  can  be  realized  only  by  seeing  the  structures  themselves. 
Another  thing  to  be  kept  hi  mind  is,  that  parts  which  are  represented  in 
engravings  with  definite  lines  for  the  sake  of  distinctness,  are  ordinarily 
not  thus  distinct  in  the  structures.  To  make  them  so,  the  dissecting- 
knife  must  separate  them,  and  take  off  the  cellular  substance,  which,  as 
the  general  packing  material  of  the  body,  everywhere  connects  adjacent 
parts  together.  » 

The  teacher  can  be  aided  very  much  in  giving  his  scholars  a  correct 
idea  of  different  organs,  by  presenting  to  them  organs  taken  from  the 
bodies  of  animals.  Thus,  in  giving  them  an  idea  of  the  lungs,  the 
lungs  of  a  calf  or  a  sheep  can  be  used.  A  pipe  may  be  fastened  into 
the  windpipe  ;  and  by  blowing  into  this,  you  can  show  how  the  lungs  are 
inflated.  An  idea  of  the  appearance  of  the  human  brain  can  be  given  by 
means  of  the  brain  of  a  calf,  or  any  other  animal  of  sufficient  size. 
An  ox's  heart  may  be  used  in  showing  the  structure  and  arrangement 
of  the  valves  and  other  parts  of  that  organ,  for  they  are  essentially  the 
same  as  in  man.  A  very  good  idea  of  the  arrangement  of  the  cartilages 
that  make  up  the  larynx,  can  be  obtained  from  the  larynx  of  an  ox  or 
cow.  The  general  shape  and  arrangement  are  the  same  as  in  man.  It 
is  some  trouble  to  clear  the  parts  of -muscular  substance,  but  the  teacher 
can  get  some  physician  or  medical  student  to  do  it  for  him.  When  the 
preparation  is  once  made,  it  tan  be  dried  for  permanent  use.  I  have  one 
which  I  made  twenty-five  years  ago.  In  drying,  it  will  be  necessary  to 
keep  the  wings  of  the  thyroid  cartilage  apart  by  a  wedge,  and  the 
supple  epiglottis  must  be  placed  in  such  a  position  as  not  to  interfere 
with  a  view  of  the  interior  of  the  larynx.  The  large  eye  of  the  ox  can 
be  made  use  of  to  show  the  various  parts  of  that  organ,  and  also  to 
show  the  formation  of  the  images  of  objects  on  the  retina. 

One  great  advantage  of  thus  using  parts  from  different  animals  is, 
that  a  taste  is  given  for  the  examination  of  the  phenomena  of  life,  with 
its  wonderful  mechanisms,  wherever  they  may  be  seen.  All  living  na- 
ture thus  becomes  full  of  suggestive  interest  to  the  young  student. 

There  are  some  things  of  which  plates  can  give  no  correct  idea. 
Such,  for  example,  is  the  cellular  membrane.  The  attempt  to  represent 
it  is  made  in  most  books  on  physiology,  but  it  is  an  entire  failure. 
I  have  a  plate  representing  its  cells  as  seen  in  a  dried  preparation  under 
the  microscope  ;  but  to  give  the  scholar  an  idea  of  it  as  it  appears  to  the 
naked  eye  in  its  natural  condition,  I  refer  him  to  it  as  seen  in  any  com- 
mon piece  of  meat  between  the  muscles  and  between  the  fibres  of  each 
muscle.  The  teacher  can  use  a  piece  of  meat  for  this  purpose.  The 
difference  between  muscles,  tendons,  and  ligaments  can  be  shown  in  the 
same  way. 

Those  figures  which  are  mere  diagrams  it  will  be  well  for  the  scholar 
to  draw  on  the  blackboard,  and  his  skill  in  description  and  remark  may 
be  exercised  for  his  own  benefit  and  for  that  of  the  class.  He  should 


APPENDIX.  413 

be  trained  in  this  exercise  in  such  a  way,  that  he  will  acquire  the  power 
of  giving  well-proportioned  and  well-arranged  descriptions,  without  the 
aid  of  prompting  by  minute  questions  from  the  teacher. 

It  will  be  proper  to  say  something  of  the  use  which  should  be  made 
of  the  questions  that  I  have  prepared.  I  have  two  reasons  for  not 
placing  them  at  the  foot  of  the  page.  One  reason  is,  that  the  book 
is  designed  for  general  reading  as  well  as  for  instruction.  But  the 
chief  reason  is,  that  I  wish  to  prevent  a  too  free  use  of  questions  on  the 
part  both  of  teacher  and  scholar.  The  marking  with  the  pencil  of  parts 
which  contain  the  answers  to  the  questions,  so  often  done  in  our 
schools,  should  never  be  permitted  by  the  teacher,  for  reasons  that  I 
need  not  stop  to  notice. 

The  scholar  should  read  the  text  at  first  without  reference  to  the 
questions  ;  and  then  the  questions  can  be  made  use  of,  perhaps  with 
profit,  to  fix  definitely  in  the  mind  the  principal  points  that  are  brought 
out.  It  will  be  a  useful  exercise  for  the  scholar,  after  reading  a  page  or 
two,  to  think  over  the  main  points,  and  then  see  by  the  aid  of  the  ques- 
tions whether  any  important  point  has  escaped  his  recollection,  or  failed 
to  make  the  proper  impression  on  his  mind. 

The  questions  that  I  have  constructed  will,  I  think,  be  found  to  be 
fitted  to  the  great  majority  of  scholars.  But  of  course  the  teacher  will 
vary  them  to  suit  the  different  capacities  and  mental  attitudes  which  he 
finds  in  his  class. 

It  is  best  not  to  have  an  uniform  mode  of  asking  questions,  even  with 
the  same  scholar.  Variety  should  be  given  to  the  mode  of  hearing  the 
recitation.  Sometimes  the  questions  should  be  minute,  and  at  other 
times  the  mind  of  the  scholar  should  be  left  to  go  on  with  as  little  lead- 
ing as  possible. 

The  scholar  should  be  encouraged  occasionally  to  give  the  substance 
of  a  whole  paragraph,  or  even  of  more  than  this.  In  doing  so,  any 
failure  in  arrangement  or  proportion  can  be  noticed  by  the  teacher,  for 
the  benefit  not  only  of  the  scholar  that  is  reciting,  but  also  of  the  whole 
class.  The  general  scope  of  an  argument  may  also  be  given  in  the 
same  way,  and  the  manner  of  doing  it  be  made  the  subject  of  criticism. 

The  numbers  attached  to  the  questions  refer  to  the  pages,  this  being 
more  convenient  to  the  scholar  than  a  numbering  by  paragraphs  wuoiu 
be,  though  of  course  it  cannot  be  quite  as  definite  in  all  cases. 

35* 


414  APPENDIX. 


QUESTIONS. 


CHAPTER  I. 

13.  In  what  respect  are  a  crystal  and  a  plant  alike  1     How  do  they 
differ  in  the  modes  of  their  formation  1     What  different  offices  do  the 
organs  in  a  plant  perform  1     What  is  meant  when  we  call  the  plant  an 
organized  substance,  and  the  crystal  an  unorga?iizcd  substance  1 

14.  Do  the  organs  in  the  plant  act  wholly  on  mechanical  principles  1 
Or  on   chemical  1     What  principles  control  the  mechanical  and  the  che- 
mical 1     What  two  classes  are  there  of  organized  living  beings  1     How 
do  they  differ  as  to  the  complex  character  of  their  organization  1     Under 
what  two  grand  divisions  do  you  class  all  the  substances  of  the  mate- 
rial world  1     How  do  plants  and  animals  differ  from  minerals  as  to  the 
parts  of  which  they  are  composed  1 

15.  What  is  assimilation  1     Explain  it  as  it  takes  place: — First,  in 
the  plant,  and  secondly,  in  the  animal.     How  do  organized  and  unor- 
ganized substances  differ  as  to  permanency  1     Point  out  the  mode  and 
the  extent  of  the  change  that  occurs  in  the  organized. 

16.  Why  is  there  more  change  in  animals  than  in  plants  1      How 
can  minerals  be  changed  1     Are  they  productive,  as  animals  and  plants 
arel      Contrast    organized   and   unorganized  substances  in   regard  to 
change  in  the  phenomena  that  you  see  in  the  world  around  you. 

17.  How  do  organized  and  unorganized  substances  differ  as  to  regu- 
larity in  form  1     What  does  irregularity  in  the  unorganized  arise  from  ? 
How  does   the   law   of  regularity  operate   in   organized   substances  ? 
Does  the  exactness  which  it  sometimes  shows  appear  in  straight  or  in 
curved  lines  1 

18.  In  which  is  the  regularity  the  most  wonderful,  the  organized  or 
the  unorganized,  and  why  1     Give  the  four  reasons  assigned  : — First,  as 
to  change  ;  secondly,  as  to  variety  of  form  ;  thirdly,  as  to  its  continu- 
ance from  age  to  age ;  and  fourthly,  as  to  its  preservation  in  the  midst 
of  a  certain  range  of  irregularity. 

19.  Exemplify  the  last  point  by  reference  to  the  human  countenance. 
How  is  the  law  of  regularity  exemplified  in  the  two  halves  of  the  body  1 
Mention  some  organs  which  are  destitute  of  this  symmetry ;  mention 
also  some  animals  that  do  not  exhibit  it.      What   is   the  distinction 
between  organized  and  unorganized  substances  as  to  limit  of  size  1 

20.  How  do  organized  and  unorganized  substances  differ  as  to  their 
structure  1     How  do  they  differ  as  to  the  number  of  elements  of  which 
they  are  composed  1     What  are  the  four  principal  elements  of  organ 


APPENDIX.  415 


ized  bodies  1  Which  one  of  these  is  solid  1  In  what  form  are  the  other 
three1?  How  many  elementary  substances  are  there  in  the  material 
world  1  How  many  of  these  are  found  in  plants  and  animals  1 

CHAPTER  II. 

21.  Point  out  the  difference  between  the  plant  and  the  animal  as  to 
locomotion.     How  does  this  difference  make  it  necessary  that  the  ani- 
mal should  have  a  stomach  1     Trace  the  analogy  between  the  stomach 
in  the  animal  and  the  roots  in   the   plant.      What   is  the  difference 
between  most  animals  and  plants  as  to  central  organs  1     What  is  their 
difference  as  to  the  effect  of  mutilation  upon  them  1 

22.  What  is  the  distinction  between  animals  and  vegetables  as  to  sen- 
sation and  spontaneous  motion  1      Have  all  animals  consciousness  and 
thought 7     Name  some  exceptions  to  the  distinction  as  to  locomotion. 
What  is  the  difference  between  the  motions  of  such  plants  as  the  sensi- 
tive-plant and  catch-fly,  and  those  of  animals  1     Make  the  comparison  in 
relation  to  the  hydra,  which  describe. 

23.  Can  the  distinction  as  to  a  digestive  cavity  always  be  made  out  1 
If  it  could  be,  should  it  be  considered  an  essential  distinction  1     What  is 
the  really  essential  distinction  between  animals  and  plants  1     What  part 
of  the  structure  of  animals  is  peculiar  to  them  1     Has  this  structure 
ever  been  discovered  in  any  plant  1     Why  ought  we  to  be  able  to  dis- 
cover it  in  the  sensitive-plant  and  catch-fly,  if  it  were  the  cause  of  their 
motions  1 

24.  Is  the  nervous  system  necessary  to  the  carrying  on  of  nutrition  1 
What  are  the  functions  of  organic  life  1     WThat  of  animal  life  1     W7hat 
is  the  order  of  action  in  the  nervous  system  1     In  what  respect  is  this 
order  not  observed  in  some  cases  1     Give  some  examples  of  instinctive 
and  automatic  motion.     How  does  the  heart  differ  from  the  muscles  of 
breathing  as  to  the  influence  of  sensation  and  of  the  will  on  its  action  1 

25.  What  is  the  office  of  the  central  organs  of  the  nervous  system 
in  sensation  and  motion  1     In  proportion  to  what  is  the  chief  central 
organ,  the  brain,  found  developed!     Describe  in  general  the  difference 
in  development  between  the  nervous  system  and  the  system  of  nutri- 
tion in  different  animals.     Does  the  nervous  system  undoubtedly  exist 
in  those  animals  in  which  it  cannot  be  found  1 

26.  What  reason  have  we  to  attribute  to  such  animals  the  exercise  of 
thought,  will,  and  consciousness  1     Illustrate  by  reference  to  the  Hydra. 

27.  What  is  the  distinction  between  animals  and  plants  as  to  their 
chemical  composition  1     In  which  is  carbon  the  characteristic  element, 
and  in  which  is  it  nitrogen  1     From  what  organs  in  animals  is  carbon 
thrown  off?     In  what  organs  in  plants  is  it  absorbed"? 

CHAPTER  III. 

27.  How  is  man  commonly  classed  in  the  animal  kingdom1?     On 
what  ground  can  the  classification  be  claimed  to  be  correct  1     Does  this 
classification  recognize  at  all  the  essential  distinctions  between  man  and 
other  animals  1     What  are  those  distinctions  1 

28.  Should  the  received  classification  be  considered  as  giving  man  hie 
true  position  in  the  scale  of  being  1     What  bearing  has  man's  immor 


416  APPENDIX. 


tality  on  this  subject  1  Is  the  difference  between  man  and  other  ani- 
mals like  that  which  we  see  between  different  animals  1  Is  it  a  mere 
difference  of  degree  ?  What  notice  should  the  naturalist  take  of  the 
difference  1 

29.  What  is   the    distinction  made   in  the  common   classification 
between  man  and  such  animals  as  apes  and  monkeys '!    Can  these  animals 
be  properly  said  to  have  four  hands  1     How  do  the  hands  which  they  are 
said  to  have  resemble  the  hand  of  man,  and  how  do  they  differ  from  it  ! 

30.  What  is  said  by  Sir  Charles  Bell  about  the  hand  !     What  by 
Aristotle,  and  by  Anaxagoras  1     State  some  particulars  in  which  the 
structure  of  man  differs  from  that  of  the  inferior  animals. 

31.  What  relation  have  the  peculiarities  of  man's  organization  to  his 
mental  peculiarities'?     Why  is  it  important  that  the  essential  distinc- 
tions between  man  and  animals  should  be  prominently  taught  1     What 
is  the  theory  of  Robinet ? 

32.  What  is  the  teaching  of  a  true  science  in  regard  to  the  Creator's 
agency  1     What  is  the  theory  of  gradations  in  nature  1     What  are  the 
objections  fatal  to  this  theory,  as  stated  in  §491 

33.  What  are  the  real  gradations  in  nature  1     Are  these  gradations 
in  each  of  the  kingdoms  regular  1     Is  man  inferior  to  some  animals  in 
certain  endowments]     Give  some  examples.     Is  it  strictly  true  that 
man  is  the  most  perfect  of  animals  1     In  what  respect  is  there  a  grada- 
tion in  the  three  kingdoms  of  Nature  1     Is  all  Nature  wholly  tributary 
to  man  1 

CHAPTER  IV. 

35.  Of  what  advantage  is  it  to  the  student,  in  studying  human  physi- 
ology, to  observe  the  analogies  in  the  processes  of  life  between  man  and 
other  living  beings  or  things  1  What  is  the  difference  between  Anatomy 
and  Physiology'? 

36.  What  functions  distinguish  animals  from  plants  1    Into  what  two 
classes  of  subjects  is  Physiology  naturally  divided  1     Remark  on  the 
wide  range  of  subjects  presented  in  Physiology.     In  what  respect  does 
this  study  differ  from  all  others  1 

37.  Of  what  two  parts  is  bone  composed  1     What  are  the  propor- 
tions of  these  parts  in  childhood — in  adult  age — and  in  old  age  1     How 
can  you  obtain  these  parts  separate  from  each  other  1     What  is  the 
animal  part  of  bone!     What  relation  does  this  sustain  to  the  mineral 
part  1     What  is  the  arrangement  of  the  two  parts  of  bone  in  the  very 
young  child  !     What  is  true  of  the  skeleton  of  many  fishes  1 

38.  Mention  some   cartilages  that   never  have  any  mineral  matter 
deposited  in  them.     With  what  are  the  bones  joined  together!     By 
what  are  they  moved  1     How  do  muscles  act  1     What  is  the  office  of 
the  tendons  1     What  is  their  structure  1     What  is  the  most  common 
texture  or  tissue  of  the  body  1     Why  is  it  called  areolar  or  cellular  / 
How  can  you  get  the  best  idea  of  this  texture  ]     Mention  its  different 
uses! 

39.  In  what  portions  of  the  body  is  this  tissue  most  abundant1?     In 
what  ways  does  the  free  communication  between  the  cells  of  this  tissue 
become  manifest  to  us  1     How  is  its  elasticity  affected  by  dropsy  in  it  1 

40.  What  are  the  uses  of  the  fat  deposited  in  the  cells  of  this  tissue'1 


*  APPENDIX.  417 

What  fact  is  stated  in  regard  to  hybernating  animals  1  How  is  the  fat 
kept  from  oozing  through  the  pores  of  its  cells'!  What  cavities  does 
the  mucous  tissue  line  1  How  is  the  secretion  of  mucus  effected  ?  What 
is  its  chief  use  ? 

41.  What  parts  of  organs  are  lined  by  the  serous  tissue  1     In  what 
important  respect  do  serous  membranes  differ  from  mucous  !     What  is 
the  appearance  of  the  serous  membranes  1     How  is  dropsy  produced  in 
them  ?     Are  the  organs  of  the  body  composed  of  many  tissues  1     Take 
the   stomach   as    an   example,    and  describe   its    structure.      Give  a 
summary  of  the  nutritive  functions  as  described  in  §  69. 

CHAPTER  V. 

42.  Give  a  summary  of  the  processes  of  digestion. 

43.  Of  what  substances  is  the  body  of  a  tooth  composed,  and  how 
are  they  arranged?     What  are  the  different  shapes  of  teeth,  and  for 
what  different  purposes  are  they  fitted  1     How  do  the  teeth  of  carnivor- 
ous   animals   differ   from  those  of  the   herbivorous?     How  does   the 
motion  of  the  lower  jaw  differ  in  the  two  classes  1 

44.  What  is  the  shape  of  the  teeth  in  the  insectivorous  1     What  in 
the  frugivorous  1     What  is  the  peculiar  arrangement  of  the  enamel  in 
the  teeth  of  the  herbivorous,  and  for  what   purpose?     What   can  be 
inferred  about  an  animal  from  an  examination  of  his  teeth'!     Why  is 
man  said  to  be  an  omnivorous  animal  1     Why  are  his  tearing  teeth  less 
in  length  and  in  power  than  those  of  carnivorous  animals  1 

45.  What  has  the  common  whale  in  place  of  teeth  1     What  is  the 
purpose   of  the  arrangement  1     What   supplies  the  place  of  teeth  in 
birds  ?     What  is  the  use  of  the  saliva  1     Describe  the  situation  and 
arrangement  of  the  glands  that  supply  this  fluid. 

46.  How  much  saliva  is  secreted  by  the  salivary  glands   during  a 
meal  1     Why  is  more  saliva  than  usual  needed  when  one  is  speaking  1 
What  effect  does  motion  of  the  mouth  have  on  the  secretion?     How 
are  these  salivary  glands  affected  by  tobacco-chewing  ? 

47.  Explain  the  influence  of  sympathy  in   the  secretion  of  saliva. 
What  are  the  two  kinds  of  fluid  secreted  by  the  salivary  glands,  and 
what  is  the  purpose  of  each  kind  ?     Describe  the  various  parts  engaged 
in  the  act  of  swallowing,  as  represented  in  figs.  10  and  11. 

49.  Describe  the  arrangement  of  muscular  fibres  in  the  oesophagus. 

50.  What   is  the   character   of  the  gastric  juice?     By  what  is   it 
formed  ?     Describe  the  appearance  of  the  mucous  membrane  of  the 
stomach,  as  seen  by  Dr.  Beaumont,  in  the  case  of  Alexis  St.  Martin. 
To  what  is  the  amount  of  gastric  juice  proportioned  ?     What  is  the 
effect  of  stimulating  the  stomach  to  too  large  a  secretion  of  it  from  day 
to  day  ?     What  is  the  nature  of  its  action  on  the  food  ?     How  is  the 
application  of  it  to  all  portions  of  the  food  secured  ? 

51.  Describe  the  arrangement  of  the  muscular  fibres  of  the  stomach, 
and  the  manner  of  their  action.     What  is  the  chyme  ?     What  is  the 
arrangement  of  the  valve  called  the  pylorus  ? 

52.  When  is  the  pylorus  especially  in  action  ?     If  there  be  difficulty 
in  digesting  the  food,  what  is  the  effect  on  the  action  of  this  valve? 

53.  What  are  the  different  theories  in  regard  to  the  process  of  diges- 
tion ?     What  is  the  true  character  of  the  process  ?     What  is  the  conso 

34 


4  I  <Q  APPENDIX. 


quence  if  fresh  food  be  introduced  into  the  stomach  while  the  process  is 
going  on  1  Why  is  the  practice  of  eating  between  meals  a  bad  one  1 
Why  does  eating  fast,  do  harm!  What  effect  has  great  variety  in 
food  ]  How  does  exercise  affect  digestion  1  Relate  the  experiment 
with  the  two  dogs,  and  state  what  it  proves. 

54.  What  shows  that  hunger  does  not  arise  from  emptiness  !     What 
that  it  does  not  arise  from  the  irritation  of  the  gastric  juice!     What  is 
the  cause  of  hunger  1     What  is  the  seat  of  the  sensation  !     Upon  what 
does  the  degree  of  hunger  depend  1     What  must  be  the  state  of  the 
stomach  to  have  this  sensation  exist  1 

55.  How  do  mental  impressions  sometimes  destroy  the  sensation  of 
hunger  1     How  does  food  remove  it  so  much  before  any  nourishment  is 
diffused  through  the  system  1     What  is  the  cause  of  thirst  1     Where  is 
its  seat  1 

57.  Describe  the  arrangement  of  the  digestive  organs  as  seen  in  fig. 
16.     What  are  the  uses  of  the  mesentery!     Where  are  the  bile  and 
the  fluid  secreted  by  the  pancreas  mingled  with  the  chyme  1     What  is 
one  of  the  offices  which  they  execute  ! 

58.  What  is  the  chyle  !     What  are  the  lacteals  1     What  glands  do 
they  enter  !     After  passing  on  from  these  glands,  into  what  duct  do  they 
empty  the  chyle  !     What  is  the  size  of  this  duct,  and  where  does  it 
pour  its  contents  ! 

59.  Describe  the  operation  of  the  suction  power  at  the  mouth  of 
the  thoracic  duct.     What  becomes  of  the  chyle  thus  forced  into  the 
blood  !     Why  is  the  mucous  coat  of  the  intestine  full  of  folds  ! 

60.  What  is  the  general  rule  by  which  the  variation  in  the  digestive 
apparatus  in  different  animals  is  governed  !     Exemplify  by  a  compari- 
son between  herbivorous  and  carnivorous  animals.     What  is  the  length 
of  the  alimentary  canal  in  the  lion  !     What  in  the  sheep  !     What  in 
man  !     In  what  animals  is  the  stomach  most  complicated  !     Describe 
the  apparatus  of  digestion  in  the  sheep,  and  its  successive  processes. 

62.  WThich  of  the  four  cavities  in  the  sheep's  stomach  is  the  real  sto- 
mach 1     Into  which  cavity  does  fluid  matter  always  go  !     What  is  the 
arrangement  when   the   animal  is  suckling!     Describe  the  digestive 
apparatus  of  birds  as  exemplified  in  the  turkey. 

63.  What  circumstances    govern    the    variations  of  the   digestive 
organs  in  different  animals  !     What  is  true  of  the  stomach  in  the  lower 
orders  of  animals  !     What  peculiarity  is  there  in  the  Hydra  in  regard 
to  its  stomach  ! 

CHAPTER  VI. 

64.  What  are  the  different  parts  of  the  apparatus  of  the  circulation  1 
Describe  the  agency  of  each  in  circulating  the  blood. 

65.  What  relation  does  the  heart  bear  to  the  rest  of  the  circulating 
apparatus  !     What  is  the  difference  between  the  arteries  and  the  veins 
in  their  structure  !     What  two  reasons  are  there  for  this  difference  \ 
What  is  the  pulse  ! 

66.  How  do  the  arteries  and  veins  differ  in  the  mode  of  their  divi- 
sion !     How  does  the  venous  system  differ  from  the  arterial  in  capacity  ! 
How  in  regard  to  rapidity  of  flow  of  the  blood  !     Describe  the  valves  in 
the  veins. 


APPENDIX.  419 


67.  Why  are  these  valves  needed  1     Why  is  it  more  dangerous  to 
wound  an  artery  than  a  vein  ]     Give  some  examples,  showing  how  on 
this  account  the  arteries  are  seated  more  deeply  than  the  veins. 

68.  Where  are  the  arteries  superficially  situated,  and  why  1     Describe 
the  common  mode  of  bleeding  from  the  arm.     What  is  the  proper  way 
to  stop  bleeding  from  an  artery  1 

69.  What  is  an  aneurism]     When  a  ligature  is   tied  around  the 
artery  above  an  aneurism  in  a  limb,  how  is  the  limb  to  be  supplied  with 
blood  1     What  is  the  chief  agent  in  the  circulation  of  the  blood  1     How 
can  you  illustrate  the  contraction  and  the  dilatation  of  the  heart  1 

70.  What  phenomena  show  that  the  blood-vessels  exert  an  active 
agency  in  circulating  the  blood  1     How  does  the  circulation  through  the 
liver   show  that  the   capillaries  are   active   agents  in  circulating  the 
blood  1 

71.  Why  are  the  veins  generally  full  of  blood  after  death,  while  the 
arteries  arc  nearly  empty  1 

72.  What  is  the  origin  of  the  term  artery  1     Why  do  we  not  in  com- 
mon language  speak  of  the  blood  as  running  in  the  arteries  as  well  as 
in  the  veins  1     When  did  Harvey  discover  the  circulation  of  the  blood  1 
What  is  the  color  of  the  blood  in  the  arteries !     What  color  has  it  in 
the  veins  1     Where  is  it  changed  from  red  to  purple  1     What  other 
changes  besides  that  of  color  take  place  1     What  would  be  the  conse- 
quence if  the  dark  venous  blood  should  be  sent  to  the  brain  1 

73.  Where  is  the  change  in  the  blood  from  purple  to  red  effected  1 
How  is  the  apparatus  arranged  so  as  to  send  the  purple  blood  to  the 
lungs  to  be  changed  1     Explain  the  diagram  showing  the  plan  of  the 
two  circulations. 

74.  WThat  is  the  difference  in  the  two  circulations  as  to  the  color  of 
the  blood  in  the  veins  and  the  arteries  1     What  is  the  difference  betweer. 
the  change  of  the  blood  in  the  capillaries  of  the  lungs,  and  that  which 
takes  place  in  the  capillaries  of  the  general  system  1     Describe  the  parts 
of  the  right  half  of  the  heart  as  represented  in  Fig.  26. 

75.  Describe  the  manner  in  which  the  auricle  and  ventricle,  with  the 
valves,  act.     Give  the  illustration  as  represented  in  Fig.  27. 

76.  What  is  the  difference  in  size  and  strength,  between  the  auricle 
and  ventricle  1     What  is  the  size  of  the  heart  1     Describe  the  arrange- 
ment of  the  valves  of  the  aorta. 

77.  Describe  the  special  provision  to  prevent  leaking  in  these  valves. 
How  are  the  walls  of  the  heart  supplied  with  blood  1 

78.  Describe  the  valves  between  the  auricles   and    the     ventricles. 
"Why  are  they  regulated  by  muscles  ? 

79.  WThy  are  there  no  valves  where  the  blood  pours  into  the  auricle 
from  the  vense  cavse  1     Describe  the  parts  of  the  heart  as  represented  in 
Fig.  31. 

81.  Describe  the  circulation  as  given  in  the  map  of  the  heart  in 
Fig.  32. 

82.  Describe  the  situation  of  the  heart  and  its  blood-vessels,  as  repre- 
sented in  Fig.  33. 

83.  How  do  the  four  parts  of  the  heart  act  without  disturbance1! 
What  is  the  difference  between  the  two  sounds  of  the  heart  1     What  is 
the  cause  of  the  first  sound  1     What  of  the  second  1     How  is  the  pulse 
produced  1     Explain  the  impulse  of  the  heart  against  the  chest. 


420  APPENDIX. 

84.  Explain  the  plan  of  the  pericardium. 

85.  Has  the  heart  any  repose  1      Give  some  calculations  as  to  the 
amount  of  work  it  does  in  a  lifetime. 

CHAPTER  VII. 

86.  What  two  objects  are  effected  by  the  respiration  1     Of  what  are 
the  lungs  composed  1     To  what  is  their  spongy  lightness  owing  1    How 
minute  are  the  air-cells  or  vesicles  1     In  what  way  is  the  change  pro- 
duced by  the  air  in  them  upon  the  blood  ] 

87.  Describe  the  arrangement  of  the  larynx,  the  trachea,  the  bronchi, 
and  the  lungs,  as  exhibited  in  Fig.  36.     How  are  the  heart  and  the 
lungs  arranged  in  the  chest  1 

88.  What  is  the  pleura  1     Why  are  the  lungs  not  fastened  to  the 
walls  of  the  chest  1     Describe  the  manner  in  which  the  air  is  made  to 
enter  the  chest  in  breathing.     Describe  the  framework  of  the  chest,  as 
represented  in  Fig.  37.     How  are  both  lightness  and  strength  secured 
in  this  structure  1 

89.  Why  are  the  ribs  joined  to  the  breastbone  by  means  of  carti- 
lages 1      What  is  the  chief  connecting   material  of  this  framework1! 
What  is  the  diaphragm,  and  how  is  it  arranged  1 

90.  How  does  the  diaphragm  act 1     Describe  inspiration  and  expira- 
tion as  illustrated  by  Figs.  38  and  39. 

92.  In  what  way  do  other  muscles,  besides  the  diaphragm,  act  in  res- 
piration 1     Describe  their  arrangement  and  action,  as  represented  in 
Fig.  40. 

93.  What  is  the  arrangement  of  the  muscular  fibres  between  the  ribs, 
and  their  mode  of  action  1     In  what  directions  are  the  ribs  moved  by  the 
muscles  in  the  neck  and  between  the  ribs  1     Do  these  muscles  act  much, 
if  at  all,  in  ordinary  easy  respiration  1     Under  what  circumstances  do 
they  act  strongly  1 

94.  If  air  were  admitted  to  the  outside  of  the  lungs  by  openings  in 
the  walls  of  the  chest,  what  would  be  the  result  1     How  are  the  blood 
and  the  air  kept  from  mingling  in  the  lungs,  while  they  are  brought  so 
near  together  that  the  air  changes  the  blood  !     What  experiment  shows 
that  blood  can  be  acted  upon  by  air  through  pores  1     How  important  is 
the  office  of  the  air-cells  ]     What  provisions  are  made  for  securing  to 
them  sufficient  room  under  all  circumstances  1     Illustrate  by  reference 
to  the  state  of  things  in  violent  exercise. 

95.  If  the  expansion  of  the  chest  be  restrained  in  any  way,  what  in- 
fluence is  exerted  upon  the  air-cells  1     In  what  two  ways  does  violent 
exercise  injure  the  lungs  when  the  chest  cannot  be  well  expanded ! 
What  is  said  of  the  influence  of  compression  of  the  chest  in  the  pro- 
duction of  disease  in  the  female  sex  1 

96.  What  is  said  of  the  extent  to  which  compression  of  the  chest  is 
often  carried  1 

97.  What  is  said  of  the  gradual  moulding  of  the  chest  by  continued 
compression  during  its  growth  1     How  is  death  produced  in  drowning  1 
How  is  water  prevented  from  getting  into  the  lungs  in  any  quantity  ] 
If  arterial  blood  could  be  supplied  to  all  the  organ*  while  the  breathing 
is  stopped,  what  would  be  the  result  1     What  contrivance  has  the  whale 
for  this  purpose  1 


APPENDIX.  421 


98.  What  is  the  arrangement  of  the  gills  of  a  fash  1     By  what  expe- 
riment can  you  prove  that  it  is  the  air  in  the  water  that  acts  on  the 
blood  in  the  gills,  and  thus  keeps  the  fish  alive  1     Why  cannot  the  fish 
use  air  that  is  not  mingled  with  water  1    What  provision  in  the  land-crab 
enables  him  to  live  in  air  as  well  as  in  water  1     Describe  the  arrange- 
ment of  the  gills  in  the  lob-worm,  and  the  larva  of  the  May-fly. 

99.  Hov»  are  the  respiratory  organs  arranged  in  insects  1     What  is 
the  effect  of  covering  their  stigmata  with  varnish  1 

100.  For  what  two  purposes  is  the  apparatus  of  respiration  largely 
developed  .in  birds  1     What  special  arrangement  is  there  for  securing 
lightness  1 

101.  By  what  experiment  can  you  show  that  carbonic  acid  is  thrown 
off  from  the  lungs  1     What  are  the  components  of  the  air,  and  what  is 
their  proportion  !     Which  of  these  is  essential  to  life  1     Why  would  it 
not  be  well  to  breathe  pure  oxygen  alone  1     Where  has  it  been  sup- 
posed till  recently  that  the  oxygen  of  the  air  unites  with  carbon  to  make 
carbonic  acid  1     Where  does  this  union  take  place  1 

102.  What  facts  settle  the  last  question  1     Does  the  change  effected 
by  the  air  upon  the  blood  in  the  lungs  take  place  to  some  extent,  when 
blood  drawn  from  a  vein  is  exposed  to  air  1     What  experiment  illus- 
trates the  manner  in  which  the  air  acts  on  the  blood  in  the  lungs  1 

103.  How  much  carbon  is  contained  in  the  carbonic  acid  thrown  off 
from  the  lungs  in  twenty-four  hours  1     What  effect  does  this  gas  produce 
upon  the  health  if  ventilation  be  imperfect  1 

104.  What  becomes  of  the  carbonic  acid  thrown  off  from  the  lungs 
of  animals  1     How  is  the  air  replenished  with  oxygen  1     How  is  the 
equilibrium  preserved  in  different  climates  1     What  effect  has  light  upon 
the  discharge  of  oxygen  from  the  leaves  of  plants  1     By  what  process 
is  the  heat  of  the  body  maintained  1     Trace  its  analogy  to  ordinary  com- 
bustion. 

105.  What  was  formerly  supposed  in  regard  to  the  place  of  the  pro- 
duction of  animal  heat  1     What  objection  was  made  to  this  supposi- 
tion 1      Where  was  it  at  length  discovered  that  the  heat  is  made  ? 
What  are  the  three  sources  of  fuel  for  keeping  up  the  animal  heat  1 
Why  is  so  large  a  quantity  of  oily  food  eaten  in  cold  climates  1     How 
do  cold  and  tropical  climates  differ  in  the  provisions  of  nature  in  this 
respect  1 

106.  How  is  the  use  of  fat  in  maintaining  heat  exemplified  in  hiber- 
nating animals  1     Whence  comes  the  heat  produced  by  exercise  1    Why 
is  heat  in  different  animals  proportioned  to  their  degree  of  activity  1 
Contrast  the  warm  and  cold-blooded  animals  in  this  respect. 

107.  What  is  the  ordinary  temperature  of  the  human  body  1     What 
is  essential  to  comfort  as  to  temperature  in  man  1     Detail  experiments 
which  show  how  high  a  degree  of  temperature  can  be  borne. 

108.  How  are  the  evil  effects  of  excessive  heat  in  such  cases  chiefly 
prevented  1      How  much  does  the  state  of  torpidity  vary  in  different 
animals  1     On  what  does  the  degree  to  which  a  deprivation  of  air  can  ba 
borne  depend  1 

109.  How  are  some  strange  recoveries  from  drowning  to  be  explained  1 
How  far  are  the  chemical  changes  described  in  this  chapter  dependent 
on  nervous  action  1 

36 


422  APPENDIX. 


CHAPTER  VIII. 

109.  By   what   is   the   building  and   repairing  of  the  body  done 
Have  the  vessels  by  which  this  is  done,  the  power  of  selecting  their  m* 
terial  from  the  blood  1 

110.  Illustrate  the  variety  of  structures  formed  from  the  blood  by 
taking  the  eye  as  an  example.     Give  examples  of  the  co-operation  of 
the  formative  vessels  in  their  work. 

111.  How  is  the  concert  of  action  in  these  vessels  illustrated  in  the 
definite  but  various  shapes  of  the  structures  which  they  make  1     How 
is  the  wonderfulness  of  this  co-operation  shown  by  comparison  with 
the  formation  of  a  crystal  1 

112.  Illustrate  the  agreement  necessary  between  different  neighbor- 
ing sets  of  formative  vessels  in  the  process  of  growth.     Illustrate  the 
wonderfulness  of  the  concert  of  action  in  the  formative  vessels,  when 
there  is  a  change  of  action.     How  is  this  exemplified  in  certain  ani- 
mals, as  the  frog  and  the  silkworm  1 

114.  How  is  this  change  of  action  exemplified  in  the  enlargement  of 
communicating  arteries,  after  tying  an  artery  in  case  of  an  aneurism  1 

115.  Describe  the  agreement  of  action  seen  in  the  successive  changes 
that  take  place  in  the  formation,  discharge,  and  healing  of  an  abscess. 

116.  Notice  the  agreement  of  action  between  the  formative  vessels 
and  the  absorbents  in  the  cases  mentioned.     Are  the   secretions  of 
organs  made  from  the  same  material  that  the  organs  themselves  are  1 
What  exception  is  there  1 

117.  How  many  kinds  of  waste  particles  are  there  1     By  what  ab- 
sorbents are  those  particles  taken  up  that  can  be  used  again  !     What 
organs  probably  fit  them  to  be  used  again  as  a  part  of  the  building  ma- 
terial !     Where  is  the  lymph,  which  they  compose,  mingled  with  the 
blood  ? 

118.  By  what  are  the  particles  that  are  wholly  useless  absorbed  1    By 
what  organs  are  they  excreted  or  thrown  off  from  the  body  •     Do  these 
various  organs  excrete  different  parts  of  this  waste  1     Do  we  know  why 
this  waste  matter  is  introduced  into  the  blood,  instead  of  being  thrown 
off  in  some  more  direct  manner  ?     Give  some  examples  in  which  other 
functions  besides  excretion  are  performed  by  the  same  organ. 

119.  What  are  the  various  functions  of  the  skin  1     Describe  its  struc- 
ture to  show  how  well  it  is  fitted  for  these  functions. 

120.  How  extensive  is  the  tubing  of  the  sweat-glands  1     In  what  two 
respects  is  the  excretion  from  them  important  1     What  is  the  difference 
between  insensible  and  sensible  perspiration  1     What  are  the  sebaceous 
glands'!     What  purpose  do  they  serve]     Where  are  they  most  abun- 
dant 1 

121.  Upon  what  does  the  rapidity  of  the  change  constantly  going  on 
in  the  body  chiefly  depend  1     W'hich  has  the  most  influence  on  this 
change,  mental  or  bodily  labor  1     Illustrate  the  influence  of  activity  on 
this  change  by  a  comparison  between  the  frog  and  the  canary  bird. 

122.  Illustrate  the  same  influence  by  a  comparison  between  different 
parts  of  the  body.     Why  does  the  change  of  the  particles  vary  much  in 
rapidity  at  different  times  1     W7hat  is  said  of  the  mingling  of  life  and 
death  in  the  changes  of  the  particles 7 


APPENDIX.  423 


CHAPTER  IX. 

123.  What  has  been  the  common  idea  about  what  are  called  forma 
tive  vessels  '!     By  what  are  all  the  minute  operations  of  the  system  per- 
formed !     How  do  the  cells  differ  from  the  cells  in  the  cellular  tissue  1 

124.  What  do  these  cells  contain  ]     What  is  to  be  said  of  their  form 
Describe  them  as  seen  in  the  blood.     Of  what  are  the  solid  parts  of  the 
body  composed ! 

125.  How  do  the  cells  appear  as  seen  in  the  Hydra"!     Upon  what 
does  the  character  of  many  of  the  textures  of  the  body  depend  1     What 
is  the  chief  difference  between  the  various  glands  of  the  body  1     Upon 
what  do  the  colors  of  various  parts  depend  !     How  are  the  colors  of 
flowers  varied  in  kind  and  in  degree  1 

126.  Illustrate  the  selecting  power  of  the  cells.     Can  we  account  for 
this  power '?     What  is  said  of  the  idea  that  the  selection  is  the  result 
of  atfinity  1     What  is  said  of  the  changes  that  take  place  in  the  con- 
tents of  the  cells  1     In  what  two  ways  do  cells  produce  other  cells  1 

127.  How  many  kinds  of  cells  are  there  in  the  blood  1     What  gives 
the  red  color  to  the  blood  1     What  are  two  of  the  offices  of  the  colored 
cells  1     How  does  their  amount  vary  in  different  animals,  and  in  differ- 
ent individuals  of  the  human  race  ] 

128.  DescriBl  by  the  figure  the  manner  in  which  absorption  is  per- 
formed on  the  surface  of  the  mucous  membrane  in  the  bowels. 

129.  Describe  in  like  manner  secretion  by  Fig.  63. 

130.  Of  what  is  the  cuticle  or  scarfskin  composed  1      How  many 
fibrilla  are  there  in  a  muscular  fibre]     What  is  each  one  of  these 
fibrillae  1      What  takes  place   in   them    when   the  muscle   contracts  ? 
What  is  the  cause  then  of  the  swelling  out  of  a  muscle  when  it  acts  1 
How  minute  are  the  cells  in  muscles  1 

131.  What  solid  animal  deposits  are  made  by  cells]     Describe  tho 
arrangement  in  the  enamel  of  the  teeth.     Of  what  are  the  nerves  com- 
posed ! 

132.  What  has  been  found  in  regard  to  combinations  between  the 
tubuli  of  the  nerves  1      How  are  these  tubuli  made  from  cells  1     In 
what  other  parts  of  the  nervous  system  besides  the  nerves,  are  they 
found  '?     What  is  the  office  of  the  tubuli  1     What  is  the  office  of  the 
gray  substance  of  the  brain  1     Of  what  is  this  substance  chiefly  com- 
posed 1     What  is  said  of  the  form  of  its  cells  1     Where  does  the  micro- 
scope show  us  is  the  beginning  of  life  1 

133.  What  is  the  extent  of  the  agency  of  the  cells  1     In  the  forma- 
tion of  every  animal  what  precedes  the  appearance  of  any  diversity  of 
parts  1 

134.  Describe  the  arrangement  of  the  contents  of  an  egg. 

135.  Describe  the  succession  of  processes  that  take  place  in  the  yolk 
preparatory  to  the  formation  of  the  bird.     From  what  material  are  all 
the  parts  of  the  bird  made  1 

136.  What  is  the  allantois,  and  what  is  its  office  1     How  can  you 
prevent  it  from  performing  its  office,  and  thus  arrest  the  development  of 
the  animal  !     When  the  bird  is  fully  formed,  how  is  he  enabled  to  burst 
the  shell '!     What  is  the  grand  distinction  between  organized  and  unor- 
ganized substances  I 


424  APPENDIX. 


137.  What  comparison  is  made  between  gravitation  and  cell-life? 
Compare  the  exhibition  of  the  Creator's  power  in  the  minute  and  in  the 
large  operations  of  nature.  What  comparison  can  you  make  between 
the  beauty  of  nature  as  seen  by  the  naked  eye,  and  its  inner  beauty 
revealed  by  the  microscope  1 

CHAPTER  X. 

139.  How  far  are  the  functions  of  nutrition  alike  in  animals  and 
plants  1     How  has  the  microscope  shown  formation  to  be  essentially  the 
same  in  both  1     Through  what  system  are  the  uses  for  which  the  body 
is  constructed  secured  ? 

140.  Why  are  the  functions  that  are  performed  through  the  nervous 
system,  called  functions  of  animal  life  1     Why  are  they  also  called  func- 
tions of  relation  1      Through  what  intermediate  instruments  does  this 
system  perform  its  functions  1     How  does  this  system  vary  in  compli 
cation  in  different  animals  1 

141.  How  much  is  learned  through  the  nerves  and  their  subordinate 
organs,  the  organs  of  the  senses  1     Mention  the  subjects  to  be  treated 
of  in  this  third  part  of  the  book.     What  are  the  three  parts  into  which 
the  nervous  system  may  be  divided! 

142.  What  three  things  are  necessary  to  sensation  V  Illustrate  the 
necessity  of  each.     What  three  things  are  necessary  to  voluntary  mo- 
tion 1     Describe  the  arrangement  of  the  parts  of  the  nervous  system  as 
represented  in  Fig.  72. 

144.  Describe  the  arrangement  and  structure  of  the  brain  as  repre- 
sented in  Fig.  73. 

145.  What  part  of  the  nervous  system  is  most  immediately  essential 
to  the  continuance  of  life  1     And  why ?     Illustrate  by  facts.     What  are 
the  convolutions  of  the  brain  1     Describe  the  membranes  of  the  brain — 
the  pia  mater — the  dura  mater — the  arachnoid. 

146.  What  is  the  consistence  of  the  brain  1     What  is  the  arrange- 
ment of  the  gray  and  the  white  substance  ? 

147.  Does  the  arrangement  of  the  convolutions  favor  the  idea  of  the 
phrenologist  1     Of  what  is  the  white  substance  of  the  brain  composed  1 
What  function  is  performed  by  it  1     What  tubuli  transmit  impressions 
from  the  brain  1     What  transmit  to  it?     What  is  said  of  the  size  of  the 
tubuli  1 

148.  What  is  the  function  of  the  gray  substance  1     In  proportion  to 
what  does  its  amount  vary  in  different  animals  1     Is  there  gray  matter 
at  the  extremities  of  the  nerves  1 

149.  With  what  are  the  cells  in  the  gray  substance  mingled?     What 
is  said  of  the  necessity  of  a  supply  of  arterial  blood  to  this  substance  ? 
How  does  the  arrangement  of  the  gray  and  the  white  substance  differ 
in  the  brain,  in  the  spinal  marrow,  and  in  the  ganglions  ?     What  are 
ganglions  ?     What  are  plexuses  ? 

150.  Why  is  the  gray  matter  so  largely  supplied  with  blood  ?     What 
has  the  microscope  shown  in  regard  to  the  changes  going  on  in  this  sub- 
stance ?     What  is  said  of  the  manner  in  which  the  nerves  terminate  in 
the  organs  of  the  body  ? 

151.  Where  are  the  Pacinian  corpuscles  mostly  found?      Describe 
their  structure.     What  do  we  know  of  their  use  ? 


APPENDIX.  425 


152.  What  is  there  that  is  wonderful  in  the  healing  of  a  divided 
nerve  1     What  do  the  observations  of  M.  Sequard  show!     What  fact 
was  proved  by  the  experiments  of  Dr.  Haighton  1     What  does  this  fact 
show '! 

153.  What  nervous  changes  occur  when  a  union  takes  place  between 
parts  that  do  not  belong  together  1     Do  the  same  nerves  answer  for  sen- 
sation and  for  motion  !     In  what  part  of  the  body  are  nerves  of  differ- 
ent kinds  kept  separate  1     How  is  it  in  all  other  parts  1     What  is  the 
arrangement  of  the  nerves  that  branch  out  from  the  spinal  marrow  1 
What  two  purposes  do  the  two  roots  of  each  nerve  serve  !     How  is  this 
ascertained ! 

154.  Are  there  different  nerves   for  different  kinds   of  sensation11 
How  is  it  in  the  eye]     How  in  the  nose  !     What  is  a  nerve  of  common 
sensation!     What  is  a  nerve  of  special  sensation  1     Is  each  nerve  fitted 
for  its  own  peculiar  office  1     Illustrate  by  reference  to  the  nerves  of  the 
eye.     Notice  particularly  the  effects  produced,  if  the  nerve  of  common 
sensation  in  the  eye  be  paralyzed. 

155.  Why  are  different  parts  of  the  body  endowed  with  different  de- 
grees of  sensibility  1     What  organ  is  more  sensitive  than  any  other  1 
How  much  sensibility  have  the  muscles  !     How  much  have  the  bones  1 
What  fact  is  related  to  show  the  use  of  the  sensibility  of  the  skin  in 
preventing  injury  !     What  change  takes  place  in  the  sensibility  of  inter- 
nal parts  when  they  become  inflamed!     What  benevolent  purpose  is 
there  in  this  1     Does  a  nerve,  as  a  matter  of  course,  have  sensibility  ! 

156.  What  is  true  of  the  brain  in  relation  to  sensibility  1     What  of 
the  heart  1     Relate  the  case  given  in  illustration.     Is  the  heart  well  en- 
dowed with  nerves  1     With  what  nerves  is  it  endowed  1     What  is  said 
of  the  nerves  of  motion  in  the  face"?     What  are  the  appearances  when 
the  nerve  of  expression  in  the  face  is  paralyzed !     Why  is  this  nerve 
called  the  respiratory  nerve  of  the  face! 

157.  How  are  the  motions  of  expression  in  the  face  connected  with 
the  motions  of  respiration  1     Describe  the  results  when  this  connection 
is  broken  by  a  paralysis  of  the  respiratory  nerve  of  the  face. 

158.  How  many  different  nerves  are  devoted  to  the  eye!     What  are 
their  different  offices !     Of  nerves  going  to  the  same  part  may  one  be 
palsied  while  another  is  not !     Give  some  illustrations.     Give  the  case 
related  by  Sir  C.  Bell. 

159.  Are  the  nerves  of  different  kinds  all  alike  in  their  structure  and 
composition!      Why  cannot  the   impression  producing   sensation  be 
transmitted  by  the  same  nerve  with  the  impression  producing  motion ! 

160.  What  has  been  till  recently  the  most  common  theory  in  regard 
to  the  action  of  the  nerves !     Upon  what  circumstances  is  the  opinion, 
that  nerve-force  is  identical  with  electricity,  based !     Mention  the  facts 
and  experiments  that  disprove  this. 

161.  In  what  direction  is  nervous  action  in   sensation  ?      In  what 
direction  is  voluntary  motion !     Does  voluntary  motion  occur  sometimes 
in  consequence  of  sensation,  and  sometimes  not !    Illustrate  this.    Give 
the  resemblance  of  the  nervous   system  to   a   telegraphic  apparatus. 
What  is  true  of  motion  caused  by  mental  emotions! 

162.  Give  some  examples  of  muscles  that  are  wholly  involuntary,  and 
of  muscles  that  are  partially  so.     What  is  the  difference  between  an 
excitor  and  a  motor  nerve !     Illustrate  by  reference  to  the  respiration — 

3o* 


496  APPENDIX. 

the  contraction  of  the  iris — and  the  action  of  the  muscular  coat  of  the 
stomach. 

163.  Why  is  the  action  of  these  two  classes  of  nerves  called  a  reflex 
action  1     Do  we  know  what  is  transmitted  through  the  trunk  of  a  nerve  1 
Does  reflex  action  ordinarily  occur  without  positive  sensation  ?     Under 
what  circumstances  is  sensation  connected  with  it  1     Illustrate  by  refer 
ence  to  the  action  of  the  respiratory  muscles,  and  the  muscular  action 
of  the  stomach.     In  relation  to  what  class  of  muscles  does  the  spinal 
marrow  act  for  the  most  part  independently  of  the  brain  1 

164.  What  is  the  relation  of  the  spinal  marrow  to  the  brain  in  regard 
to  the  voluntary  muscles  1     What  is  true  therefore  of  injuries  of  the 
spine  1     State  now  the  two  separate  functions  of  the  spinal  marrow. 
By  what  arrangement  are  they  performed  1      Illustrate  the  modes  of 
ejecting  sensation — motion — and  reflex  action. 

165.  How  does  the  brain  differ  from  the  spinal  marrow  as  to  intervals 
of  rest  ]     Illustrate  the  continuous  action  of  the  spinal  marrow,  as  seen 
in  the  operations  that  go  on  in  the  system  when  the  brain  is  asleep,  or  is 
torpid  with  disease.     Besides  these  operations,  mention  some  of  the  mo- 
tions that  can  be  excited  through  the  agency  of  the  spinal  marrow  inde- 
pendent of  the  brain.     Explain  the  agency  of  the  spinal  marrow  in  con- 
vulsions. 

166.  What  is  said  of  the  fact,  that  in  convulsions  there  is  an  invol- 
untary action  of  muscles  that  are  ordinarily  under  the  control  of  the 
will  1     Cite  some  facts  to  show  that  voluntary  muscles  act  involuntarily 
more  often  than  is  commonly  supposed. 

167.  Explain  the  involuntary  action  of  muscles  in  walking  and  other 
like  acts.     How  is  it  with  one  who  is  walking  in  a  reverie  1     What  was 
formerly  supposed  in  relation  to  the  importance  of  the  brain  as  a  central 
organ  of  the  nervous  system  1     How  do  we  know  that  the  brain  is  not 
directly  essential  to  the  maintenance  of  life  1 

168.  What  are  the  functions  most  essential  to  life1?     Upon  what  part 
of  the  spinal  marrow  do  these  depend  1     Illustrate  the  extent  to  which 
the  different  parts  of  the  spinal  marrow  are  independent  of  each  other. 
Is  there  any  sensation  independent  of  the  brain  1 

169.  Why  is  the  system  of  nerves,  of  which  I  have  treated  in  this 
chapter,  called  the  cerebro-spinal  system  1     What  other  system  is  there  1 
What  are  its  purposes  1     What  are  its  arrangements  1     How  does  it 
differ  in  its  general  arrangement  from  the  cerebro-spinal  system  1 

CHAPTER  XL 

170.  What  two  different  purposes  do  the  bones  fulfil  1     What  bene- 
volent purpose  is  manifest  in  the  predominance  of  the  animal  portion  of 
bone  over  the  mineral  in  the  child  1     In  what  two  forms  is  bony  sub- 
stance deposited  1     How  are  these  arranged  in  the  flat  bones  1     How  in 
the  long  1 

171.  How  are  both  lightness  and  strength  secured  in  a  long  bone — 
first,  in  the  body  of  the  bone,  and  then,  in  its  ends  1     Why  are  the  eiids 
not  made  like  the  shaft  1     What  is  the  marrow  of  the  bone  1 

172.  How  is  a  bone  nourished  1     What  is  the  periosteum  1     Do  arte- 
ries enter  the  solid  substance  of  the  bone  1     Describe  the  manner  in 
which  circulation  is  carried  on  in  every  point,  as  shown  by  the  micro 
scope. 


APPENDIX.  427 


173.  What  fluid  circulates  in  the  minute  channels  in  bone,  shown  to 
us  by  the  microscope  1  What  is  said  of  the  sensibility  of  bone  ]  Give 
a  general  description  of  the  skeleton,  noticing  the  variety  of  shape  in 
the  bones,  and  the  purposes  which  they  answer. 

175.  How  many  bones  are  there  in  the  head1?     How  many  of  these 
belong  to  the  face  ?     How  many  to  the  cranium  1     Describe  the  latter, 
as  represented  in  Fig.  87. 

176.  Why  is  the  box  (as  the  cranium  may  be  called)  holding  the 
brain,  composed  of  so  many  bones  ]     Describe  the  structure  of  the  prin- 
cipal bones  of  the  cranium.     What  is  the  difference  between  the  join- 
ings of  the  outer  and  those  of  the  inner  tables  of  these  bones  1     What 
is  the  reason  of  this  difference  1 

177.  How  are  the  principles  seen  in  the  construction  of  domes  illus- 
trated in  the  cranium  ]     Of  what  bones  is  the  dome  of  the  cranium 
made  up]     Describe  the  different  ways  in  which  strength  is  secured 
around  the  base  of  this  dome.     Describe  especially  the  arrangement  be- 
tween the  parietal  and  temporal  bones. 

178.  When  violence  is  inflicted  upon  the  head,  what  is  the  direct  cause 
of  the  injurious  effects  felt  by  the  brain  1     On  what  principle  do  the 
guards  of  the  brain  defend  against  this  cause  of  injury?     Mention  now 
in  their  order  the  different  textures  through  which  the  vibration  of  a 
blow  must  pass  before  it  reaches  the  brain,  pointing  out  their  agency  in 
lessening  the  vibration. 

179.  What  arrangement  is  there  of  the  lower  part  of  the  frontal  bone 
as  a  special  guard  against  injury  at  that  point  1     How  is  the  side  of  the 
head,  so  peculiarly  exposed  to  violence,  especially  guarded1?     What  other 
organs,  beside  the  brain,  are  protected  by  the  cranium  1 

180.  Describe  the  arrangement  of  some  of  the  bones  of  the  face. 
Describe  the  cavities  of  the  nostrils,  and  the  sinuses  connected  with 
them.      What   is  the  object  of  the  great  extent  of  surface  in  these 
cavities  1 

181.  Describe  the  lower  jaw.      How  many  distinct  structures  are 
there  in  the  teeth  ]     What  is  their  arrangement] 

182.  How  does  a  tooth  differ  from  a  bone  1     What  is  the  reason  for 
this  difference1?      What  is  the  necessity  for  having  a  second  set  of 
teeth  ] 

183.  Describe  the  hyoid  bone,  its  position,  and  its  connections.    Men- 
tion other  bones  which,  like  this,  are  not  directly  connected  with  the 
bones  of  the  skeleton.     Of  .how  many  bones  is  the  spinal  column  com- 
posed]    Acting  as  the  great  pillar  of  the  body,  what  does  it  support? 
What  is  the  pedestal  on  which  it  stands,  and  in  what  manner  is  this 
pedestal  made  firm]     While  this  column  is  thus  firm,  it  needs  to  be 
flexible — how  is  this  accomplished]      Notice  its  different  degrees  of 
flexibility  in  different  portions  of  it.     WThy  is  there  so  little  motion  in 
that  portion  that  supports  the  framework  of  the  chest  ] 

184.  Besides  serving  as  a  firm  pillar  and  a  flexible  chain,  what  other 
purpose  does  the  spinal  column  fulfil  ]     Describe  a  vertebra.     By  what 
are  the  vertebrae-bound  together  ] 

185.  Describe  the  canal  in  this  column  for  the  spinal  marrow.     What 
is  the  arrangement  for  the  nerves  that  pass  from  it  ]     How  are  the  car- 
tilages arranged  ]     What  two  purposes  do  they  subserve  1 

186.  What  is  there  in  the  shape  of  the  spinal  column  that  acts  as  a 


428  APPENDIX. 

safeguard  against  shocks  to  the  brain  1  What  are  now  the  three  objects 
secured  in  the  structure  of  the  spine  1  Describe  the  contrivance  at  the 
top  of  it,  as  represented  in  Figs.  95,  96  &  97.  Compare  this  with  the 
mounting  of  a  telescope.  What  is  the  difference  in  the  two  cases  1 

188.  By  what  arrangement  is  the  freeness  of  motion  in  the  neck  of 
birds  made  consistent  with  the  security  of  the  spinal  marrow  1     What 
is  there  peculiar  in  the  spinal  column  of  quadrupeds  1 

189.  What  is  the  paxy-waxy  1     How  are  the  vertebrae  of  fishes  con- 
structed and  arranged  1     How  is  the  great  flexibility  of  the  spine  in 
reptiles  secured  1     How  in  the  neck  of  the  giraffe  1 

190.  Describe  the  arrangement  of  the  breast-bone,  the  collar-bone, 
and  the  shoulder-blades.     What  is  the  use  of  the  collar-bone,  and  what 
are  its  variations  in  different  animals  1     How  does  the  shoulder-blade 
differ  from  all  other  bones  in  the  body  1 

192.  Why  is  the  socket  of  the  shoulder-joint  so  shallow  ?     Describe 
the  arrangement  of  the  radius  and  ulna,  and  the  manner  in  which  such 
free  and  varied  motion  is  given  to  the  arm.     Describe  the  three  parts  of 
the  hand. 

193.  Describe  the  ligaments  that  bind  the  bones  of  the  hand  together. 
What  is  the  principal  object  aimed  at  in  the  construction  of  the  lower 
extremity  1     What  in  the  upper  1 

194.  Describe  the  thigh-bone.     What  is  the  patella  1      What  pur- 
poses does  it  answer  1     What  part  of  the  foot  is  formed  by  the  tarsus  1 
What  part  by  the  metatarsus  1 

195.  How  many  bones  are  there  in  the  toes'!     How  many  in  the 
whole  foot  1     What  object  is  secured  by  having  so  many  bones  in  the 
foot  1     Why  is  the  foot  arched  1     Describe  its  movement  in  walking. 
With  what  are  the  ends  of  the  bones  tipped,  and  why  1     What  is  the 
arrangement  of  the  membrane  that  lines  the  ends  of  the  bones  1 

196.  What  contrivance  is  there  in  the  knee-joint,  and  in  the  articula- 
tion of  the  lower  jaw  1 

CHAPTER  XII. 

196.  Give  the  summary  in  §  294,  in  regard  to  the  action  of  the  mus- 
cles, and  their  nervous  connections. 

197.  What  are  the  tendons  1     WThat  is  said  of  the  relation  they  bear 
to  the  muscles — their  shape — their  mode  of  union  with  muscles  and 
with  bones — their  strength — and  their  size  1     How  are  the  muscles  and 
tendons  arranged  in  reference  to  convenience  and  beauty  1     Illustrate 
by  the  arm  and  the  hand. 

198.  Illustrate  the  application  of  the  first  kind  of  lever  in  the  action 
of  muscles — so  also  of  the  second  kind. 

199.  And  of  the  third  kind.     Which  kind  is  most  frequently  used  in 
the  body  1 

200.  What  two  different  objects  are  aimed  at  in  the  application  of 
these  two  levers  1     Illustrate  by  examples  of  the  second  kind  of  lever. 

201.  Illustrate  the  same  by  examples  of  the  third  kind.     What  is  the 
difference  between  the  motion  of  the  forearm  on  the  arm,  and  the  mo- 
tion of  the  lower  jaw,  in  the  application  of  the  principles  alluded  to. 

203.  Show  how  quickness  is  secured  at  the  sacrifice  of  power  in  the 
case  of  the  biceps  muscle,  as  illustrated  in  Fig.  1 14.     Under  what  me- 


APPENDIX.  429 


chanical  disadvantage  do  most  of  the  muscles  act,  as  represented  in 
Fig.  1151 

204.  Show  by  this  figure  how  quickness  of  movement  is  gained  in 
this  case.     Why  is  the  muscle,  the  deltoid,  whose  action  is  represented 
in  this  diagram,  so  large  1 

205.  How  is  the  mechanical  disadvantage,  which  thus  results  from 
the  oblique  action  of  the  muscles,  in  part  obviated  1     Illustrate  by  Figs. 
116  &  117.     Describe  the  agency  of  the  patella  in  this  respect.     To 
what  extent  is  the  pulley  used  in  the  arrangement  of  muscles  ? 

206.  Show  the  application  of  the  pulley,  as  seen  in  the  ankle. 

207.  Describe  the  pulley  arrangement  of  the  digastric  muscle.    What 
is  the  necessity  for  such  an  arrangement  1     What  other  office  does  this 
muscle  perform,  besides  drawing  down  the  lower  jaw,  and  how  does  it 
doit! 

208.  Describe  the  muscles  that  move  the  ball  of  the  eye. 

209.  What  is  said  of  the  actions  of  opponent  muscles  1     What  is 
Paley's  comparison  1     Is  it  strictly  correct  1     Give  some  examples  of  the 
tonic  contraction  of  muscles.     What  is  the  cause  of  wry  neck,  and  of 
squinting  I     Illustrate  the  compound  action  of  muscles  by  Fig.  1 13. 

210.  How  does  variation  in  the  degree  of  the  contraction  of  muscles 
affect  the  variety  of  motion  1     What  organ  peculiarly  exemplifies  vari- 
ety in  muscular  action  1     Give  a  general  description  of  the  muscles  of 
the  body,  as  exhibited  in  Figs.  122  &  123. 

214.  What  is  said  of  the  variety  of  size  in  muscles  1     What  other 
parts  besides  the  bones  are  moved  by  muscles  1     How  are  the  muscles 
arranged  in  reference  to  convenience  and  symmetry  1 

215.  Describe  a  peculiar  arrangement  of  tendons  and  muscles  in  the 
sole  of  the  foot.     Describe  the  arrangement  of  tendons  represented  in 
Fig.  124. 

216.  Describe  the  complicated  action  of  the  muscles  in  swallowing — 
and  in  speaking  and  singing.     How  are  the  epiglottis  and  the  larynx 
used  in  these  acts  1  What  is  said  of  the  ease  and  quickness  of  the 
change  from  the  one  act  to  the  other  1 

217.  Show  how  the  variety  and  complication  of  muscular  action  are 
illustrated  in  some  of  the  general  movements  of  the  body  : — as  walking, 
pulling  with  the  feet  braced,  and  balancing.     Describe  the  operation  of 
the  toggle-joint. 

218.  Give  examples  of  the  application  of  this  operation  in  the  action 
of  muscles. 

219.  How  many  muscles  are  there  in  the  hand  and  arm'?     What  is 
said  of  the  extent  of  the  variety  of  their  action  !     Contrast  the  hand, 
as  doing  light  and  heavy  work.     Give  a  summary  of  the  endowments 
of  the  hand. 

220.  Give  a  description  of  various  muscular  movements  that  may  be 
going  on  in  the  body  at  the  same  time.     What  is  the  muscular  sense  1 

221.  Illustrate  the  operation  of  it  in  various  ways.     Is  this  sense  a 
source  of  enjoyment  1 

CHAPTER  XIII. 

222.  By  what  alone  are  thought  and  feeling  expressed!     What  sub- 
ordinate  modes  of  expression  are  there  1     Illustrate  the  fact  that  these 


430  APPENDIX. 

require  to  be  interpreted  by  muscular  action.  By  what  mode  of  muscu- 
lar action  are  thought  and  feeling  mostly  communicated  1  What  rela- 
tion has  writing  to  this  mode  of  communication  !  What  other  parts 
beside  the  face  are  brought  into  action  in  the  language  of  the  muscles  1 

223.  Illustrate  the  extent  of  this  language.    How  can  we  get  the  best 
idea  of  its  extent  ?     How  do  other  animals  differ  from  man  in  regard  to 
the  parts  used  in  the  language  of  the  muscles  1     What  passion  is  almost 
the  only  one  that  can  be  expressed  by  them  in  the  countenance  1    What 
distinction  is  sometimes  made  on  this  ground  between  man  and  other 
animals  1 

224.  What  are  the  principal  muscles  that  give  the  face  expression  1 
How  is  a  smile  produced  1     How  is  sadness  expressed  1     How  do  smil- 
ing and  laughing  differ  in  the  action  of  the  muscles'! 

225.  How  does  weeping  differ  from  mere  sadness  in  muscular  action1? 
What  peculiarity  is  there  in  muscular  action  in  weeping  from  pain  1 

226.  To  what  is  to  be  attributed  the  apparent  expression  of  the  eye  1 
How  can  it  be  proved  that  the  eye  has  no  active  agency  in  expression  1 

227.  What  is  the  common  notion  in  regard  to  the  eye  as  a  means  of 
expression  1      How  far  is  expression   a  result  of  combined  muscular 
action  ? 

228.  Describe  the  muscles  of  the  face,  with  the  action  of  each,  as  ex- 
hibited in  Fig.  130. 

229.  Describe  the  muscles  about  the  mouth,  as  shown  in  Fig.  131. 

230.  In  what  way  is  the  expression  of  the  face  made  the  same  in  its 
two  halves  1     What  nerve  governs  all  the  muscles  of  expression  in  the 
face  1     What  results  when  one  of  this  pair  of  nerves  is  paralyzed  1 

231.  Is  there  commonly  any  one  muscle  devoted  to  the  expression  of 
any  one  emotion  or  passion  1     Does  the  same  muscle  often  take  a  part 
in  the  expression  of  various  emotions  1     Explain  the  agency  of*  various 
muscles — the  frontal — the  corrugator  supercilii — the  superbus.     Illus- 
trate the  combination  of  muscular  action  in  expression,  as  shown  in  Fig. 
132,  and  also  in  Fig.  127 — giving  the  differences  in  them.     What  is  the 
action  of  the  muscles  in  quiet  sorrow  1 

233.  What   is    their   state   in  the  expression  of  a  calm   pleasure"? 
What  in  the  expression  of  admiration  1     How  does  temperament  affect 
the  state  of  the  muscles  in  the  two  last-mentioned  expressions  1     De- 
scribe the  action  of  the  muscles  in  the  expression  of  rage.     By  what 
combination  of  the  action  of  muscles  are  the  canine  teeth  exposed '? 

234.  Describe  the  action  of  the  muscles  in  fear.     Show  how  it  differs 
from  their  action  in  rage. 

235.  Illustrate  the  agency  of  the  muscles  of  the  eyeball  in  expression. 
What  is  said  of  the  action  of  the  oblique  muscles  1 

236.  Why  is  the  intoxicated  man  apt  to  squint  and  to  see  double "? 
Why  does  he  raise  his  eyebrows  in  the  effort  to  keep  his  eyes  open "? 
What  muscles  of  expression  are  found  in  the  faces  of  animals  1     In  re- 
gard to  what  muscles  is  the  horse  specially  endowed  1     What  is  said  of 
the  muscles  that  distend  the  nostrils  in  the  case  of  man  1 

237.  What  muscles  of  expression  are  wholly  peculiar  to  man  1     Re- 
mark on  each.    What  are  almost  the  only  passions  that  can  be  expressed 
by  the  faces  of  animals  1     What  special  provisions  are  there  in  some  for 
the  expression  of  rage — about  the  mouth,  and  the  eye  1    What  peculiar 


APPENDIX.  431 

phenomenon  in  the  reflection  of  light  is  seen  in  the  eye  of  the  cat  tribcj 
and  what  is  the  explanation  of  it  1 

238.  Give  the  substance  of  §  348  in  regard  to  the  combinatior  of 
muscular  action  in  the  expression  of  the  countenance.     What  is  said  in 
§  349  of  the  action  of  the  rest  of  the  body  in  expression  1 

239.  What  muscles  of  the  body  sympathize  most  with  those  of  the 
face  in  expression  1     Give  examples  in  illustration.     What  effects  are 
produced  by  mental  emotions  on  the  circulation  1     What  is  the  expla- 
nation of  blushing!     What  is  said  of  the  adaptation  of  the  countenance 
to  the  mind  as  an  instrument  of  expression'!     Draw  the  analogy  be- 
tween the  hand  and  the  face  in  this  respect. 

240.  What  is  said  of  the  importance  of  training  the  muscles  of  the 
face  1     How  far  does  beauty  of  countenance  depend  upon  muscular  ac- 
tion ]     W7hat  difference  is  there  in  this  respect  between  the  living  coun- 
tenance, and  the  face  of  a  statue  1     Give  the  remark  of  Addison. 

241.  What  is  said  of  skill  in  the  use  of  the  muscles  of  the  face  as 
compared  with  those  of  the  hand  1     In  what  cases  may  you  see  this 
skill '!     What  is  said  of  mistakes  in  interpreting  the  language  of  the 
muscles  1     WThat  is  said  of  the  influence  of  moral  and  mental  cultiva- 
tion upon  the  countenance"? 

242.  Explain  the  expression  of  the  countenance,  as  seen  after  death. 

CHAPTER  XIV. 

243.  What  principles  apply  to  the  construction  of  the  apparatus  of 
the  voice  1     Illustrate  its  superiority  to  other  instruments  as  a  musical 
instrument.     What  most  particularly  distinguishes  it  from  them? 

244.  What  is  said  of  its  power  of  fascination  1     What  comparison  is 
made  in  this  respect  between  the  voice  of  conversation  and  that  of  song  1 
What  is  said  of  the  variety  of  voices  in  the  brute  creation  1 

245.  Into  what  two  kinds  are  wind-instruments  divided  1     Explain 
the  manner  in  which  the  variation  of  note  is  produced  in  those  of  the 
first  kind,  by  reference  to  the  flute  and  the  trombone. 

246.  Illustrate  the  same  point  in  the  operation  of  the  flute-stop  of  the 
organ.     What  influence  does  the  width  of  the  vibrating  column  of  air 
have  upon  the  note?     How  is  the  note  varied  in  those  wind-instru- 
ments in  which  the  length  of  the  column  of  air  cannot  be  altered  ? 
How  are  the  variations  of  note  produced  in  whistling  1 

247.  What  are  some  of  the  wind-instruments  of  the  second  class  1 
How  is  the  sound  produced  in  these  1     How  is  the  note  varied  1     Illus- 
trate by  reference  to  the  reed-stops  of  the  organ.     How  are  the  various 
notes  produced  in  the  clarionet  1     Trace  the  analogy,  in  the  application 
of  the  principles  of  musical  sounds,  between  the  vibrating  column  of 
air,  the  reed,  and  the  strings  in  such  instruments  as  the  piano  and  vio- 
lin.    Explain  the  relation  of  the  tube  of  the  reed-instrument  to  the  reed, 
as  stated  in  §  366. 

248.  What  is  the  trachea,  and  of  what  is  it  composed  1     Why  are  its 
rings  of  cartilage  not  perfect  rings  1     What  is  the  larynx  ? 

249.  Describe  the  parts  of  the  larynx  as  represented  in  Fig.   136. 
Describe  particularly  the  arrangement  of  the  arytenoid  cartilages  and 
the  vocal  ligaments,  as  represented  in  Figs.  137  &  138. 

250    Describe,  by  means  of  Fig.  137,  the  manner  in  which  the  differ- 


432  APPENDIX. 


ent  notes  of  the  voice  are  produced.     Describe  the  apparatus  of  the 
voice,  as  represented  in  Fig.  139. 

252.  What  is  the  arrangement  of  the  two  pairs  of  ligaments  1 

253.  How  do  we  know  that  the  lower  ligaments  are  the  true  vocal 
cnords  1     Apply  now  the  principles  regulating  the  variation  of  note  in 
common  musical  instruments  to  the  vocal  apparatus. 

254.  Give  Magendie's  experiment.     What  is  said  of  the  question  as 
to  what  kind  of  musical  instrument  the  larynx  most  resembles  1     Give 
the  general  conclusion  as  to  the  application  of  the  great  principle  of 
musical  sounds.     What  is  the  tube  of  the  vocal  apparatus,  which  an- 
swers to  the  tube  of  a  reed-instrument  1     How  many  outlets  has  it  1 
From  which  does  the  voice  generally  issue  1     How  is  it  in  humming  1 

255.  What  influence  do  the  cavities  of  the  nose  have  on  the  voice  1 
In  what  way  is  the  reverberation  in  them  regulated]     In  what  two 
ways  is  the  size  of  the  vibrating  column  of  air  in  the  tube  of  the  vocal 
instrument  varied  1     What  influence  does  this  tube  have  on  the  charac- 
ter of  the  voice  1     How  would  the  voice  sound  if  it  should  come  directly 
from  the  larynx,  instead  of  passing  through  the  tube  attached  to  it  1 

256.  What  is  the  cause  of  alterations  in  the  voice,  as  hoarseness  1 
Where  is  the  difficulty  when  the  voice  is  lost  1     In  what  two  ways  does 
the  epiglottis  affect  the  voice  1 

257.  What  is  said  of  the  variety  and  precision  of  the  action  of  the 
muscles  in  the  modulation  and  articulation  of  the  voice  1     How  much 
do  the  ligaments  vary  in  length  in  producing  all  the  variety  of  notes  of 
which  the  voice  is  capable  1     Give  the  calculation  in  regard  to  the  mi- 
nuteness of  the  muscular  action  in  passing  from  one  note  to  another. 
How  does  the  vocal  instrument  differ  from  others  in  the  mode  of  pass- 
ing from  one  note  to  another  1     With  what  instrument  can  the  voice  be 
imitated  in  this  respect  1     How  does  the  voice  of  speech  differ  from  thai 
of  song! 

258.  What  is  said  of  the  training  of  the  muscles  of  the  vocal  appara- 
tus !     What  is  the  analogy  between  the  training  of  the  muscles  moving 
the  vocal  ligaments,  and  the  training  of  the  lips  in  playing  on  a  reed- 
instrument  1     What  is  said  of  skill  in  managing  the  muscles  of  the 
chest  in  speaking  and  singing  1     Give  the  illustration  of  the  bag-pipe 

259.  What  is  one  of  the  chief  causes  of  "throat  disease"  in  public 
speakers  1     What  circumstances  tend  to  produce  this  disease  1     Where 
is  the  voice  formed  in  birds  1     How  is  the  vocal  tube  in  their  case  altered 
in  its  length  for  the  different  notes  1 

260.  Describe  the  various  parts  of  the  vocal  tube,  that  have  an  agency 
in  articulation.     In  the  articulation  of  how  many  letters  is  the  tongue 
the  chief  agent  1     State  some  facts  to  show  that  the  tongue  is  not  so 
essential  to  the  power  of  speech  as  is  commonly  supposed. 

261.  What  letters  are  chiefly  formed  by  the  teeth"?     What  is  lisp- 
ing 1     What  letters  are  chiefly  formed  by  the  lips  1 

262.  Why  do  children  use  labials  so  early  and  so  freely  1     Of  what 
are  their  terms  of  endearment  composed  in  most  languages  1      Give 
other  facts  stated  in  this  paragraph  in  relation  to  the  use  of  labials. 
Illustrate  the  agency  of  the  nasal  cavities  in  articulation.     What  consti- 
tutes a  distinguishing  peculiarity  of  many  consonants'! 

263.  Explain  the  difficulty  called  speaking  through  the  nose.     What 
is  said  of  articulation  in  whispering  1 


APPENDIX.  433 


264.  How  is  the  variation  of  note  in  whispering  caused  ]     How  can 
you  observe  the  mechanism  of  the  parts  necessary  in  producing  any  of 
the  alphabetic  elements  !     What  is  said  of  the  common  definition  of 
consonants  ]     Mention  some  of  the  attempts  that  have  been  made  to 
imitate  the  articulation  of  the  voice  by  mechanism. 

265.  How   many   alphabetic   elements   are    there,    as    reckoned    by 
Rushl     By  what  is  the  adjustment  of  the  articulating  apparatus  for 
each  one  of  them  effected  1     What  is  said  of  the  training  of  the  mus- 
cles of  the  voice  1     Describe  the  process  of  learning  to  talk  in  the  child. 

266.  What  is  the  chief  instructor  of  the  voice  1     What  other  organ 
assists  in  this  instruction  1     Illustrate  the  fact  that  it  is  difficult  for  any 
but  the  young  to  acquire  accurately  the  pronunciation  of  a  language. 
What  is  said  of  skill  in  the  use  of  the  vocal  apparatus ]     Compare  this 
with  skill  in  the  use  of  other  muscles. 

267.  What  is  stammering]     What  facts  are  stated  in  regard  to  it 7 
In  deaf  mutes  what  is  the  cause  of  the  dumbness  in  almost  every  easel 
What  cases  may  be  cited  in  proof]     Give  the  case  related  by  Magendie. 

268.  What  other  cases  maybe  cited  that  are  more  common'?     Can 
deaf  mutes  be  taught  to  talk  !     What  objections  are  there  to  doing  if? 

269.  Explain  the  difference  between  the  voice  of  speech  and  that  of 
song.     Illustrate  the  uses  of  the  vanishing  movement  in  speech. 

270.  What  effect  does  the  use  of  the  vanish  on  the  interval  of  a  semi- 
tone produce  ]     Illustrate  this.     What  two  reasons  are  given  for  the  fact 
that,  while  every  one  learns  to  talk,  there  are  many  that  do  not  learn  to 
sing] 

271.  How  is  musical  talent  compared  with  other  talents  1     What  is 
the  explanation  of  ventriloquism  1 

CHAPTER  XV. 

271.  How  is  sound  produced1?     When  is  sound  musical,  and  when 
discordant  1 

272.  What  is  said  of  the  transmission  of  sound "?     What  of  its  re- 
flection ]     Illustrate  the  influence  of  the  reflection  of  sound  in  accumu- 
lating it. 

273.  How  can  you  prove  that  sound,  unlike  light,  cannot  be  trans- 
mitted through  a  vacuum  1     What  is  true  of  the  facility  of  the  transmis- 
sion of  sound  through  solids  and  fluids  as  compared  with  air  1     Illus- 
trate it  by  facts.     How  is  the  fact,  that  sonorous  vibration  does  not  rea- 
dily pass  from  one  medium  to  another,  illustrated  1     Upon  what  does  the 
degree  to  which  the  vibration  is  lessened  in  passing  from  one  substance 
to  another,  depend] 

274.  In  what  cases  is  the  intervention  of  a  membrane  of  essential 
service,  and  why  1     Give  a  general  description  of  the  process  of  hear- 
ing.    Describe  the  apparatus  of  hearing,  as  represented  in  Fig.  148. 

275.  What  is  the  object  of  the  external  ear  ]     What  is  the  use  of 
its  ridges  and  prominences  ] 

276.  What  is  said  of  the  external  ears  of  animals  in  comparison  with 
man  ]     Describe  the  tube  of  the  ear.     By  what  two  means  is  it  guarded 
against  intruders  ]     Describe  the  drum  of  the  ear  and  the  little  bones. 

277.  What  is  the  arrangement  of  these  bones  1     What  are  their  con- 
nections, and  how  do  their  muscles  act  upon  them  ]     How  does  the  cav- 

37 


434  APPENDIX. 


ity  of  the  tympanum  communicate  with  the  mouth,  and  why  1  What 
part  of  the  ear  is  the  essential  part  of  the  apparatus  1  How  much  of 
the  apparatus  may  be  destroyed  without  entire  loss  of  hearing  !  Give 
the  case  related  by  Sir  Astley  Cooper. 

278.  Describe  the  parts  of  the  labyrinth.     In  what  different  ways 
may  deafness  be  produced  by  defects  in  this  part  of  the  apparatus  1 

279.  Why  is  it  better  that  the  vibrating  substance  in  the  labyrinth  be 
a  fluid  than  a  solid  or  a  gaseous  substance1!     What  is  the  use  of  the 
chain  of  bones  1     Describe  the  chalky  concretions,  and  their  use. 

280.  What  is  the  use  of  the  fencstra  rotunda  1    Describe  the  arrange- 
ment of  the  cochlea. 

281.  In  what  two  directions  is  the  vibration  of  the  fluid  in  the  laby- 
rinth transmitted!     What  is  the  course  of  the  vibration  in  the  cochlea] 
What  is  the  arrangement  of  the  membranes  in  the  cavities  of  the  laby- 
rinth 1    What  is  the  arrangement  of  the  nerves  in  the  semicircular  canals  1 

283.  Describe  the  distribution  of  the  nerve  in  the  cochlea.     In  what 
two  ways  does  the  nerve  here  receive  impressions  from  the  vibration  of 
the  fluid  1 

284.  Describe  now,  step  by  step,  the  process  of  hearing.     Is  all  our 
hearing  done  in  this  way!     Give  examples  of  hearing  through  the  bone 
enclosing  the  labyrinth.     How  does  the  apparatus  of  hearing  in  fishes 
differ  from  that  of  man  1     Why  is  it  less  complicated  than  in  animals 
that  live  in  air  1 

285.  Mention  some  particulars  in  which  the  ear  of  birds  differs  from 
that  of  man.      What  is  the  simplest  form  of  the  hearing  apparatus 
found  in  animals  1     What  are  some  of  the  suppositions  in  regard  to  the 
offices  of  particular  parts  of  the  labyrinth  1     What  is  true  of  them  1 
What  part  of  the  process  of  hearing  can  we  trace  and  understand! 
How  much  do  we  know  about  the  transmission  of  the  impression  from 
the  fluid  through  the  nerve  to  the  mind ! 

286.  Is  it  true  that  the  eye  is  a  more  wonderful  organ  than  the  ear! 
What  is  said  of  the  mingling  of  the  spiritual  and  the  simply  mechani 
cal  in  the  process  of  hearing !     What  are  to  be  considered  the  two  ends 
of  the  apparatus  of  hearing ! 

CHAPTER  XVI. 

287.  Into  what  two  parts  may  the  process  of  seeing  be  divided  1 
What  principles  govern  the  construction  of  the  mechanical  part  of  the 
apparatus !     What  is  the  object  of  its  arrangements !     How  is  the  sec- 
ond part  of  the  process  executed!     How  does  the  transmission  of  light 
resemble  that  of  sound!     What  is  the  refraction  of  light!     Illustrate 
by  Fig.  156. 

288.  How  are  the  rays  bent  in  relation  to  a  perpendicular  when  they 
pass  from  a  denser  into  a  rarer  medium !     How,  when  they  pass  from 
a  rarer  into  a  denser!     How  are  the  rays  refracted  when  they  pass 
through  a  medium  that  presents  a  convex  surface! 

289.  How  are  the  rays  refracted  when  they  pass  through  a  medium 
which  has  a  concave  surface  ! 

290.  How  many  coats  has  the  eye !     Describe  the  arrangement  of 
the  parts  of  the  eye,  as  represented  in  Fig.  159.     What  is  the  use  of 
the  sclerotic  coat !     How  is  the  cornea  fitted  into  it !     What  is  the  colo> 


APPENDIX.  435 


of  the  choroid  coat,  and  to  what  is  it  owing  ?  Of  what  is  the  retina 
chiefly  composed  1  What  are  the  three  .humors  of  the  eye  1  Describe 
the  chamber  in  which  the  aqueous  humor  is.  What  is  the  consistence 
of  the  crystalline  immor  or  lens  ?  Describe  the  vitreous  humor.  Why 
is  it  called  vitreous  ? 

291.  Describe  the  various  parts  as  they  are  more  minutely  delineated 
in  Fig.  160.     How  is  the  aqueous  humor  formed  1     How  is  it  continu- 
ally changed  1     Describe  the  membrane  called  the  conjunctiva.     Wrhat 
are  the  ciliary  processes  1     Describe  their  arrangement. 

292.  What  is  their  use  1     How  are  images  of  objects  formed  upon  the 
retina  1     How  can  the  fact,  that  such  images  are  formed,  be  proved 7 

293.  Why  are  these  images  inverted  1     What  is  the  plan  of  a  camera 
obscura  1     Compare  the  eye  in  its  arrangements  to  an  instrument  of 
this  kind. 

294.  What  qualities  are  needed  in  the  cornea?     How  is  its  transpa- 
rency secured  1     Why  is  it  more  convex  than  the  sclerotic  coat  1     On 
what  does  the  color  of  the  iris  depend  1     What  is  the  principal  office  of 
the  iris  1     By  what  arrangement  of  its  muscular  fibres  are  its  motions 
effected?     How  does  the  pupil  differ  in  carnivorous  and  herbivorous 
animals  1 

295.  What  is  the  office  of  the  crystalline  lens  1     What  is  its  shape  1 
Its  structure  1     What  disease  has  its  seat  here  1     What  are  the  three 
modes  of  remedying  the  difficulty  1     What  two  purposes  does  the  cho- 
roid coat  serve  1     Why  is  its  color  dark  1 

296.  What  is  the  state  of  the  choroid  coat  in  the  albino  1     What 
gives  the  bright  red  or  pinky  hue  to  the  iris  in  his  case  1     How  does  the 
color  of  the  choroid  coat  vary  in  different  animals  1     What  is  the  cha- 
racter of  the  retina,  and  its  office  1     Trace  the  analogy  between  the 
optic  nerve  and  the  other  nerves  of  sense  1     What  resemblance  is  there 
to  the  nerve  of  touch  in  its  termination  ?    What  is  the  defect  in  the  opera- 
tion of  optical  instruments,  called  spherical  aberration,  and  how  is  it 
obviated  in  the  eye  1 

297.  What  is  the  difficulty  in  the  operation  of  a  common  lens,  called 
chromatic  aberration  1     How  is  this  obviated  in  the  lens  1     How  in  the 
eye? 

298.  Contrast  the  eye  with  the  telescope  in  regard  to  the  facility  with 
which  the  eye  accommodates  itself  to  objects  at  different  distances.     In 
what  two  ways  is  this  accommodation  effected  ? 

299.  By  what  defects  in  the  structure  of  the  eye  in  the  near-sighted 
is  this  power  of  adjustment  counteracted  ?     How  is  this  difficulty  obvi- 
ated ?     In  what  way  is  near-sightedness  often  produced  ?     What  is  the 
difficulty  in  the  far-sighted  ?     How  is  it  obviated  ?     At  what  different 
periods  of  life  are  these  two  defects  apt  to  appear,  and  why  ?     How  is 
the  fact,  that  objects  appear  in  their  right  position,  although  their  images 
are  inverted  on  the  retina,  sometimes  accounted  for  ? 

300.  What  objection  is  there  to  this  explanation  ?     Upon  what  erro- 
neous idea  are  such  explanations  based  ?     Do  we  really  know  how  the 
mind  gets  the  right  idea  of  the  relative  position  of  objects  ? 

301.  What  is  necessary  to  single  vision  in  regard  to  the  two  images 
formed  in  the  two  eyes  ?     Why  do  you  see  double  when  you  press  one 
of  the  eyes  a  little  out  of  its  place  ?     What  is  necessary  to  single  vision 
In  the  action  of  the  muscles  ?     Why  does  the  intoxicated  man  often  see 


436  APPENDIX. 

confusedly,  or  even  sometimes  double  1  Relate  and  explain  the  case 
given  to  show  how  disease  may  produce  double  vision.  Why  is  there 
not  double  vision  ordinarily  in  squinting  1 

302.  When  are  the  two  images  in  the  eyes  alike  1     In  what  cases  are 
they  unlike  1     Relate  the  experiment  given  in  explanation.     How  is  it 
that  in  such  a  case,  while  there  are  two  images,  and  therefore  two  im- 
pressions sent  along  the  two  optic  nerves,  yet  the  impression  on  the 
mind  is  single  1     How  does  a  person  who  has  but  one  eye,  acquire  the 
idea  of  solidity  1 

303.  Explain  Professor  Wheatstone's  stereoscope  on  the  principles 
developed  in  §  454. 

304.  Mention  the  particulars  in  which  the  harmony  of  action  in  the 
two  eyes  is  wonderful. 

305.  Notice  the  correspondence  between  the  two  eyes  in  that  part  of 
the  process  which  belongs  to  the  optic  nerves.    What  peculiarity  is  there 
in  the  arrangement  of  these  nerves  1     Do  we  instinctively  perceive  the 
size,  distance  and  figure  of  objects,  or  is  it  an  acquired  power  1     Relate 
in  illustration  the  case  given  by  Cheselden. 

306.  How  does  the  experience  thus  related  compare  with  the  experi- 
ence of  the  child  in  learning  to  see?     Give  the  analogy  between  learn- 
ing to  see  and  learning  to  walk  or  talk.     In  learning  to  appreciate  the 
sizes,  shapes  and  distances  of  objects,  what  sense  acts  as  the  educator 
of  vision  !    What  is  said  of  the  frequency  of  mistakes  in  vision  1    What 
of  okill  in  seeing  1     What  is  the  visual  angle  1 

307.  Can  we  get  a  correct  idea  of  magnitude  by  the  visual  angle 
alone  1     Illustrate  by  the  Figure.     What  circumstance  must  be  known 
in  regard  to  an  object,  in  order  to  have  our  estimate  by  the  visual  angle 
correct  1     Mention  another  means  that  we  use  in  connection  with  the 
visual  angle.     Give  examples  of  mistakes  that  we  are  apt  to  make  in 
the  use  of  this  means. 

308.  Illustrate  the  manner  in  which  we  get  ideas  of  the  magnitude  of 
objects  by  comparison.     Show  how  we  sometimes  are  made  aware  of 
our  dependence  on  this  source  of  evidence.     Why  does  the  moon  ap- 
pear so  large  when  rising  1     Explain  the  use  of  the  muscular  sense  in 
acquiring  an  idea  of  the  size  and  distance  of  objects.     What  use  is 
made  of  it  in  looking  at  very  near  objects  1     What  is  said  of  our  consci- 
ousness of  the  effort  in  doing  this  1 

309.  Why  can  you  not  judge  accurately  of  the  locality  of  very  near 
and  minute  objects  when  you  use  but  one  eye  1     What  do  we  observe 
in  regard  to  the  use  of  the  convergence  of  the  eyes,  when  we  look  at 
the  eyes  of  others  ?     How  far  is  seeing  a  mental  process  1     What  is 
said  of  the  common  notion,  that  it  is  a  simple  and  easy  process  1    What 
is  said  of  the  training  required  for  its  performance  1 

310.  Do  all  the  images  formed  on  the  retina  transmit  impressions  to 
the  mindl     Illustrate  by  reference  to   squinting.     Also   illustrate  in 
reference  to   ordinary  vision    by  an    experiment.       Explain  this  by 
Fig.  175. 

311.  Show  now  how  it  is  that,  notwithstanding  the  facts  stated  in 
§  464,  we  are  not  conscious  of  seeing  double.     Show  too  how  we  can 
by  an  effort  of  the  will  have  this  consciousness. 

312.  What  is  the  paint  of  distinct  vision,  as  it  is  called  ?     Show  hov? 
the  mental  attention  makes  use  of  this — how  in  looking  at  an  object— 


APPENDIX.  437 

in  reading — in  looking  at  a  prospect  1  Why  do  we  seem  to  see  tho 
whole  of  a  page  or  of  a  prospect  at  once  with  equal  distinctness  1 
How  far  do  we  see  the  whole  of  a  page  or  a  prospect  at  once  1  "What 
is  said  of  the  minuteness  and  correctness  of  the  pictures  formed  on  the 
retina  1 

313.  How  do  we  in  part  estimate  the  motion  of  objects  1     What  is 
said  of  the  delicacy  of  the  process  by  which  this  is  done  1     Illustrate1 
the  frequent  erroneousness  of  our  impressions  in  regard  to  motion. 

Why  is  it  that  when  we  are  moving  rapidly,  near  objects  seem  to  fly 
back,  and  distant  objects  seem  to  go  along  with  us  1  Illustrate  by  the 
Figure. 

314.  What  is  said  of  the  rapidity  with  which  impressions  received 
from  the  images  on  the  retina  succeed  each  other  1     Show  how  this 
may  be  measured  by  experiment.     To  what  is  the  difference  in  time 
required  for  distinct  transmission  in  different  individuals  owing  ]    Trace 
the  analogy  between  this  difference  a»d  that  which  we  see  in  different 
individuals  in  regard  to  the  use  of  the  muscles. 

315.  Explain  the  Thaumatrope.     How  is  the  eye  situated  so  as  to 
protect  against  injury  1     How  does  the  cushion  of  fat  on  which  it  rests 
serve  to  protect  it?     In  what  two  ways  does  the  muscle  that  closes  the 
eyelids  serve  as  a  protection  to  the  eye  1 

316.  How  is  it  protected  by  the  eyelashes  ?     How  by  the  eyebrows  1 
How  are  the  eyelids  constructed  in  reference  to  the  protection  of  the 
eye  1     How  do  the  tears  serve  as  a  protection  i     Why  do  fishes  have  no 
tear-apparatus  1 

317.  Describe  the  arrangement  of  the  tear  apparatus.     Why  do  the 
tears  overflow  the  edges  of  the  eyelids  when  they  are  abundant  1    What 
arrangement  of  glands  is  there  on  the  eyelids  ]     What  two  purposes 
does  the  oily  substance  formed  by  them  serve  1     How  are  the  tears  con- 
ducted into  the  mouths  of  the  ducts  when  the  eyelids  are  closed  1     De- 
scribe the  nictitating  membrane  in  the  eyes  of  birds. 

CHAPTER  XVII. 

,318.  Give  the  recapitulation  presented  in  §  476. 

319.  What  is  said  of  the  brain  as  the  organ  of  the  mind  1     What 
facts  show  that  motion  and  sensation  are  dependent  on  the  brain  1 
How  does  it  appear  that  the  mind  thinks  only  by  means  of  the  brain  1 
How  is  life  continued  when  sensation,  motion,  and  thought  are  stopped 
by  compression  of  the  brain  1     How  does  the  variation  of  the  degree  of 
compression  vary  the  effect  on  the  mental  functions  1     How  is  the  de- 
pendence of  the  mind  on  the  brain  shown  in  disease  1 

320.  Of  what  is  insanity  always  the  result  ?     How  do  moral  causes 
produce  it  1     If  the  mind  were  separate  from  the  body,  could  insanity 
be  produced  in  it]     Can  the  disease  in  the  organization  in  insanity, 
be  always  discovered  in  an  examination  after  death  1    Describe  the  situ- 
ation of  the  brain  and  its'  immediate  connections. 

321.  What  is  said  of  the  face  1     Illustrate  the  rapidity  of  the  commu- 
nication between  the  mind  and  the  different  parts  of  the  body.     In  exe- 
cuting muscular  motion  skilfully,  is  any  assistance  derived  from  a  know- 
ledge of  the  particular  muscles  1     By  what  arrangement  is  the  mind 
enabled  to  excite  so  accurately  the  motion  of  the  muscular  fibres  * 

87' 


438  APPENDIX. 

322.  Upon  what  besides  combined  action  in  the  muscles  doer;  the  end- 
less variety  in  motion  depend  !     Mention  some  cases  in  which  we  best 
realize  the  variety  and  accuracy  of  the  messages  sent  from  the  brain  to 
the  muscles.     What  is  said  of  the  training  of  the  organs  of  sense  and 
of  motion  ]     What  of  the  amount  of  knowledge  acquired  by  the  child 
in  the  first  years  of  his  life  1 

323.  Describe  the  training  of  the  muscles  in  the  child.     What  is  true 
of  what  is  called  native  grace  1     What  is  said  of  the  training  of  tho 
muscles  of  the  face  ! 

324.  What  is  said  of  skill  in  the  use  of  the  muscles  1     What  is  said 
of  the  training  of  the  senses  1     How  do  other  animals  differ  from  man 
at  the  first  in  the  use  of  the  muscles  and  the  senses  ]     How  do  they  dif- 
fer from  him  in  the  amount  of  skill  that  training  gives  1 

325.  Illustrate  the  fact,  that  the  senses  and  muscles  are  mutual  teach- 
ers in  their  training.     How  does  the  dependence  of  the  muscles  on  the 
senses  differ  from  that  of  the  sgpses  on  the  muscles  1     What  fact  illus- 
trates the  absolute  dependenceof  the  muscles  on  the  senses  ;     In  the 
education  of  the  muscles  and  the  senses,  what  is,  strictly  speaking, 
educated  or  trained  !     Illustrate  by  reference  to  the  idiot  and  the  deaf 
mute. 

326.  What  is  said  of  the  muscles  of  the  face  in  the  idiot  1     Why 
does  not  the  education  of  the  muscles  extend  to  those  that  are  involun- 
tary 1 

327.  What  difference  is  there  in  the  different  stages  of  the  training 
of  the  muscles  in  the  degree  of  cognizance  which  the  mind  takes  of 
their  action  1     Illustrate  by  reference  to  learning  to  walk,  to  read  and  to 
sing.     What  has  been  the  general  belief  in  regard  to  the  means  of 
communication  between  different  minds  { 

328.  What  is  claimed  by  some  on  this  point  in  regard  to  what  is 
called  animal  magnetism  1     What  has  always  been  found  to  be  true  of 
this  when  its  pretensions  are  properly  tested  ]     Illustrate  the  manner  in 
which  this  was  done  in  one  case. 

329.  What  is  s^id  of  the  illustrations  afforded  by  animal  magnetism 
of  the  influence  that  can  be  exerted  upon  the  body  through  the  mind  t 
To  what  diseased  states  is  the  condition  produced  in  the  subject  analo- 
gous 1     Does  the  explanation  of  the  phenomena  show  that  there  is  any 
true  magnetic  influence  in  the  case  1 

330.  What  is  said  of  the  mingling  of  moral  and  physical  perversion 
in  the  subjects  of  animal  magnetism]     What  is  said  of  suggestive 
influences  ! 

331.  What  is  said  of  the  exaltation  of  the  powers  of  the  senses  in 
the  subjects  of  animal  magnetism  ?     What  is  true  of  clairvoyance,  so 
called  !     What  is  said  in  the  note  of  test  evidence  I     Give  the  fact 
stated  in  illustration. 

332.  What  part  of  the  brain  has  an  especial  connection  with  the 
mind  1     What  is  the  chief  office  of  the  cerebellum  1     Give  the  evidence 
from  comparative  anatomy  on  which  this  poiut  is  settled.     What  expe- 
riments lead  to  the  same  conclusion  1     What  two  reasons  are  given  why 
the  evidence  on  this  point  from  disease  is  defective]     What  fact  haa 
been  observed  in  cases  of  disease  of  the  cerebellum'!     What  negative 
testimony  is  sometimes  afforded  by  disease  in  regard  to  the  office  of  the 
cerebellum  i 


APPENDIX.  439 


333.  Give  the  summary  of  results  arrived  at  by  studying  the  compar- 
ative physiology  of  the  nervous  system,  as  stated  in  §  502.     What  is 
said  of  the  comparative  amounts  of  the  white  and  the  gray  substance  in 
the  biain  !     What  are  the  two  sources  of  evidence  in  regard  to  the  func- 
tion of  the  gray  substance  1 

334.  What  evidence  is  there  in  regard  to  phrenology  from  the  arrange- 
ment of  the  gray  substance  !     What  is  the  conclusion  from  all  the  facts 
collected  in  relation  to  the  external  examination  of  the  head  1     What 
evidence  is  the  real  test  of  the  pretensions  of  phrenology '! 

335.  What  is  true  of  the  pretended  locality  of  organs  in  the  region 
of  the  frontal  sinus  1     What  of  the  organs  said  to  be  in  that  part  of  the 
head  where  the  cerebellum  is  1     What  is  the  only  fact  that  seems  to  give 
countenance  to  phrenology  1     Why  does  this  fact  fail  to  prove  that  the 
special  seat  of  the  intellectual  faculties  is  in  the  upper  and  front  part  of 
the  head  !     What  evidence  have  we  on  this  point  from  the  phenomena 
furnished  by  disease  and  injuries  1 

336.  What  is  the  facial  angle  ?     What  is  the  difference  in  regard  to 
this  between  the  skull  of  the  European   and   that  of  the  African  t 
What  between  the  skull  of  animals  and  that  of  man!     What  is  the 
common  measure  of  this  angle  in  ancient  statues  of  deities  and  heroes] 
W'hat  is  said  of  the  rule,  that  the  amount  of  intelligence,  both  in  man 
and  in  animals,  is  proportioned  to  the  amount  of  the  cerebrum] 

337.  What  facts  show  that  size  is  far  from  being  the  only  measure  of 
power  in  case  of  the  brain  1     In  studying  the  comparative  physiology  of 
the  brain,  what  significant  fact  do  we  find  when  we  come  to  pass  from 
the  higher  animals  to  man  1     Of  what  character  is  the  mental  difference 
between  them  and  man  1     What  is  said  of  the  definiteness  of  the  dis- 
tinction between  man  and  animals  1 

338.  What  note  ought  to  be  made  of  this  distinction  by  the  compara- 
tive physiologist]     What  is  said  of  the  intimacy  of  the  union  between 
the  mind  and  the  body  1     What  might  we  infer  from  the  closeness  of 
this  union  in  regard  to  death,  if  we  had  no  Revelation  1 

339.  What  is  said  of  the  supposed  independence  of  the  mind  on  the 
body  1     Is  there  proof  that  mind  is  of  itself  indestructible  ]     What  are 
the  three  sources  of  our  knowledge  in  relation  to  the  connection  of  the 
mind  and  the  body  1     What  is  the  consequence  if  we  rely  upon  any  one 
of  these  alone  1     What  is  the  alternative  to  which  one  is  driven,  if  he 
confine  himself  to  the  evidence  which  physiology  furnishes  ]     What 
course  is  commonly  pursued  by  those  who  take  this  narrow  view  of  the 
subject] 

340.  What  is  said  of  the  distinction  between  organized  and  unorgan- 
ized matter '!     What  are  the  common  suppositions  in  regard  to  the  en- 
dowment of  organized  or  living  matter  ]     What  is  said  of  those  endow- 
ments of  living  matter  that  are  connected  with  the  nervous  system! 
What  question  now  arises  in  relation  to  intelligence  in  its  connection 
with  matter '{ 

341.  What  does  physiology  show  us  in  regard  to  this  connection! 
Point  out  the  deficiencies  of  its  teaching  in  relation  to  the  nature  of  this 
connection.     What  is  the  tendency  of  its  presumptive  evidence  1    Look- 
ing at  the  subject  solely  in  the  light  of  physiology,  what  would  be  the 
conclusion  in  regard  to  the  dependence  of  mind  on  organization,  when 
we  observe  the  origin  and  growth  of  a  thinking  animal]     What  bear- 


440  APPENDIX. 


ing  on  this  point  has  the  fact,  that  the  intellect  grows  with  the  brain,  and 
appears  at  last  to  perish  with  it  1 

342.  What  is  said  of  the  evidence  that  may  be  drawn  by  the  physi- 
ologist from  the  design  obvious  in  the  efforts  of  the  mind  !     Trace  the 
analogy,  in  this  respect,  between  mental  phenomena  and  those  that  we 
see  in  the  common  operations  of  life,  both  animal  and  vegetable.     Show 
how  the  analogy  holds  good  in  the  accommodation  to  varying  circum- 
stances in  the  cases  cited.     What  is  the  extent  of  the  analogy  seen  in 
the  phenomena  alluded  to  1     To  what  idea  has  the  contemplation  of  this 
analogy  sometimes,  led  1 

343.  Give  examples  of  phenomena  in  vegetable  life,  that  are  often 
called  instinctive.     What  fact  in  comparative  physiology  is  strongly  ad- 
verse to  materialism  1     In  which  direction,  however,  on  the  whole,  does 
the  evidence  from  physiology,  taken  alone,  preponderate  I 

344.  State  the  ground  of  the  great  need  which  the  physiologist  has 
of  the  evidence  from  other  sources  beside  his  physiology.     What  is  the 
testimony  of  consciousness  in  relation  to  the  independence  of  the  soul 
in  its  action  1     What  in  regard  to  its  responsibility  for  its  acts  1     How 
far  is  this  testimony  acted  upon  by  all,  when  physiological  speculations 
are  left  out  of  view  1 

345.  What  does  the  evidence  from  consciousness  show  us  in  relation 
to  the  connection  of  the  mind  with  the  material  organization  1     To  what 
alternative  does  it  drive  us '!     How  is  this  testimony  of  consciousness 
treated  by  the  Bible  1     Illustrate  our  dependence  on  the  Bible  for  the 
proof  of  the  soul's  immortality. 

346.  How  may  the  discrepancies  in  the  evidence  from  physiology  in 
regard  to  the  connection  of  the  mind  and  the  body  be  cleared  up  1 

347.  What  is  said  of  the  character  of  the  evidence  drawn  from  con- 
sciousness and  Revelation  1     What  is  said  of  the  presumptive  evidence 
from  physiology  in  comparison  with  it  1     W;hat  is  said  of  the  present 
moral  tendencies  of  physiological  investigations  1 

CHAPTER  XVIII. 

347.  What  was  Lord  Monboddo's  idea  of  the  development  of  man  1 

348.  What  recent  theory  has  an  analogy  to  this  1     What  is  true  of 
man  and  animals  in  relation  to  instinct  and  reason  1     Do  we  know  what 
the  nature  of  instinct  is  ]     Which  can  be  understood  best,  the  actions 
of  instinct  or  those  of  reason  1     Illustrate  this  point. 

349.  What  seems  to  produce  the  actions  of  instinct  1     Wrhat  influ- 
ence does  the  intelligence  of  the  animal  exert  upon  them  1     What  is 
said  of  the  invariableness  of  the  actions  of  instinct  1 

350.  Describe  the  nests  of  the  Baya  and  the  Tailor  Bird. 

351.  What  is  said  of  the  perfection  of  the  actions  of  instinct  1     Why 
are  the  cells  of  the  honevcomb  made  hexagonal  1     Describe  the  arrange- 
ment of  the  ends  of  these  cells.     Give  the  fact  stated  in  regard  to  the 
angle  made  by  the  surfaces  at  their  ends. 

'  352.  How  is  the  perfection  of  the  actions  of  instinct  seen  in  animals 
that  live  in  communities'!  Describe  the  structure  of  a  wasp's  nest. 
Give,  the  description  of  the  habits  of  the  beaver. 

354.  In  what  respect  may  instinct  be  said  to  be  blind  1     Illustrate  bj 


APPENDIX.  441 


reference  to  animals  that  provide  for  a  progeny  which  they  are  never  to 
see. 

355.  Why  is  it  often  difficult  to  distinguish  between  the  results  of 
reason  and  those  of  instinct  1      What  would  be  true  of  instinct  if  it 
were  at  all  rational?     Under  what  circumstances  is  there  perfection  in 
the  actions  of  instinct  1     Under  what  circumstances  does  it  fail '{     Con- 
trast instinct  and  reason  in  this  respect.     Give  some  illustrations  of  the 
characteristics  of  instinct  alluded  to. 

356.  Give  Mr.  Broderip's  account  of  the  beaver.     If  the  beaver  in  this 
case  had  been  guided  by  reason,  what  would  lie  have  done  ?     How  far 
is  the  care  that  animals  take  of  their  progeny  governed  by  a  blind 
instinct  ?     What  is  said  of  the  temporary  character  of  parental  affection 
in  their  case  1     In  what  case  is  there  no  affection  at  all  ? 

357.  What  degree  of  intelligence  is  shown  in  the  power  of  imitation 
in  animals  1     How  do  animals  show  that  they  reason '!     How  far  did  the 
beaver,  whose  story  is  given  in  $  541,  reason  1     How  does  the  character 
of  the  inferences  made  by  animals  differ  from  that  of  those  made  by 
man  1     Illustrate  by  reference  to  Newton  and  his  dog.     Of  what  are  the 
inferences  made  by  animals  the  results? 

358.  When  the  processes  of  thought  in  animals  are  extended  and 
complicated,  what  is  true  of  them  ?     Illustrate  by  examples  the  extent 
to  which  mental  association  may  be  carried  in  the  animal. 

359.  How  do  animals  learn  the  relation  of  cause  and  effect  1     Illus- 
trate by  examples.     How  does  this  knowledge  of  cause  and  effect  differ 
in  man  and  in  animals  1     Is  the  mental  difference  between  man  and 
animals  one  of  degree  only? 

360.  What  attribute  constitutes  the  great  superiority  of  the  human 
mind?     Show  how  this  attribute  is  the  origin  of  language  in  man. 
What  is  the  character  of  the  language  of  animals  ?     Why  cannot  they 
have  a  language  of  arbitrary  signs  1     What  is  the  source  of  man's  be- 
lief in  a  Creator  1     Illustrate  this  point.     Is  this  belief  implanted  in  the 
mind  1     What  two  suppositions  have  been  offered  in  relation  to  con- 
science 1 

361.  What  is  said  of  the  doubts  which  some  entertain  as  to  the  exist- 
ence of  conscience  I     What  is  true  of  those  cases  in  which  animals 
seem  to  some  to  have  a  moral  sense  1     Illustrate  the  fact  that  in  common 
language  we  recognize  the  difference  between  man  and  animals  as  to 
the  possession  of  a  conscience.     Give  a  summary  of  the  mental  differ- 
ences between  man  and  animals. 

362.  Give  the  gradations  which  we  find  in  the  nervous  system  as  wo 
trace  the  animal  kingdom  upward.     Why  does  instinct  collect  no  expe- 
rience 1     What  is  the  difference  between  the  two  kinds  of  reasoning, 
before  spoken  of,  in  collecting  experience  1     What  is  said  of  the  amount 
of  improvement  of  which  some  animals  are  capable  by  means  of  the 
lower  order  of  reasoning  1 

363.  What  is  the  basis  of  improvement  in  man  ?     What  ordinarily 
constitutes  the  intellectual  superiority  of  one  man  to  another  1     In  what 
consists  the  merit  of  an  inventor  or  discoverer?     Illustrate  by  reference 
to  Jenner.     What  is  the  difference  between  the  capabilities  of  instinct 
and  those  of  reason  in  the  rapidity  of  their  development  ?     Which  form 
of  reasoning  is  developed  first  ? 

364.  Is  the  higher  reasoning  to  some  extent  developed  quite  early  1 


442  APPENDIX. 

What  is  said  of  its  deficiency  in  those  cases  in  which  the  organization 
is  defective  1  What  is  said  of  the  achievements  of  this  reasoning  power  1 
What  of  the  separation  it  makes  between  man  and  animals  1  What  is 
said  of  the  slowness  of  development  of  man's  physical  structure1. 
What  is  the  general  law  as  to  the  development  of  capabilities,  both  men- 
tal and  physical? 

365.  What  is  said  of  the  prominence  generally  given  to  the  difference 
between  man  and  animals  in  regard  to  physical  endowments  \     Illustrate 
by  reference  to  the  hand.     In  all  animals,  to  what  are  bodily  endow- 
ments suited  1    Mentjpn  some  bodily  endowments  in  which  some  animals 
excel  man,  and  state  the  reason.     In  what  respect  is  man  most  signally 
superior  to  animals  in  physical  endowment  ]     Illustrate  this  by  refer- 
ence to  the  hand  and  the  vocal  organs. 

366.  Illustrate  the  same  point  by  the  general  motions  of  the  body. 
What  is  said  of  the  human  form  in  repose  1     How  do  we  get  the  most 
perfect  idea  of  the  superiority  of  the  human  organization  1 

CHAPTER  XIX. 

367.  Mention    some  of  the  contrasts  which  we  find  on  looking  over 
the  human  race.     How  many  varieties  of  the  race  are  commonly  reck- 
oned ]     What  are  the  characteristics  of  the  Caucasian  variety  1 

368.  What   are  the  characteristics  of  the  Ethiopian  varieties — the 
Mongolian — the  American — the  Malay  1     What  is  said  of  the  extent 
to  which  the  race  may  be  divided  into  varieties  1 

369.  What  is  said  of  the  way  in  which  national  differences  are  pro- 
duced 1     What  is  the  opinion  of  most  naturalists  in  regard  to  the  pro- 
duction of  the  races  1     What  is  the  doctrine  of  Professor  Agassis  and 
others  1     State  the  grounds  on  which  he  bases  his  doctrine. 

370.  What  is  his  opinion  in  regard  to  climatic  and  other  influences  ? 
What  is  his  opinion  of  the  history  given  in  Genesis  I     Are  the  different 
branches  of  the  race  iu  his  view  different  species,  or  mere  varieties  * 
What  is  the  distinction  between  a  species  and  a  variety  1 

371.  Mention  the  influences  included  in  the  expression,  climatic  and 
other  influences.     What  is  said  of  the  influence  of  climate  1     What  is 
the  circumstance  which  has  most  influence  in  producing  varieties  in  man 
and  in  animals  1    What  is  included  in  the  term  domestication  /    What  is 
the  precise  question  in  regard  to  climatic  and  other  influences  1 

372.  Mention  some  facts  that  show  that  climate  has  a  great  influence 
on  the  color  of  the  race.      What  influence  do  intellectual  and  moral 
causes  exert  upon  the  shape  of  the  head  1 

373.  What  is  said  of  certain  changes  in  form  produced  by  causes,  the 
operation  of  which  we  do  not  understand?     What  are  the  three  differ- 
ent types  of  form  in  the  head  stated  by  Dr.  Pritchard,  and  by  what 
causes  are  they  produced  1     State  in  regard  to  each  : — the  prognathous 
— the  pyramidal — the  oval.     Give  some  facts  showing  that  these  types 
are  convertible  into  each  other. 

374.  What  is  said  of  the  insensible  gradations  by  which  the  varieties 
of  the  race  pass  into  each  other  ?     What  two  objections  are  brought 
against  the  alleged  competency  of  climatic  and  other  influences  to  pro- 
duce the  varieties  of  the  race  ?     What  great  fact  is  a  sufficient  reply  to 
these  objections !     State  and  illustrate  this. 


APPENDIX.  443 


375.  Apply  this  fact  in  explanation  of  the  production  of  the  varieties 
of  the  human  race.     What  is  said  of  the  analogy  thus  drawn  between 
man  and  animals,  in  comparison  with  that  which  Professor  Agassis  has 
tried  to  establish  !     What  consideration  weakens  his  analogy  1 

376.  If  the  climatic  and  other  influences  appear  to  any  one  incompe 
tent  to  produce  the  varieties  of  the  race,  is  he  driven  necessarily  to  ad 
mit  its  multiple  origin  !     What  is  said  oif  the  occasional  introduction  oi 
new  causes  by  the  Creator]     Upon  what  do  our  calculations  upon  the 
regularity  of  nature  depend  1     What  is  said  of  the  change  in  the  age 
of  man  effected  at  the  time  of  the  flood !     Wrhat  is  said  of  the  occa- 
sional appearance  of  new  diseases  1 

377.  What  is  said  of  the  convulsions  which  have  evidently  taken 
place  in  the  earth  1      Does  it  make  any  difference  to  the  argument, 
whether  the  results  came  directly  from  causes,  or  from  a  chain  of  causes  1 
Apply  the  argument  to  the  production  of  the  varieties  of  the  race. 
What  is  said  of  the  objection  to  the  argument,  that  it  is  supposing  a 
miraculous  interposition  ! 

378.  Is  the  supposition  thus  made  needed!     What  is  said  of  it  in 
comparison  with  the  supposition  of  Agassis  1     On  what  principles  is  the 
testimony  of  the  Bible  as  to  the  origin  of  the  race  to  be  interpreted  I 
What  are  the  main  facts  which  it  gives  in  relation  to  it  1     How  is  the 
truth  of  its  testimony  confirmed  1 

379.  Of  what  force  is  analogical  and  presumptive  evidence  in  oppo- 
sition to  it!     Is  any  fear  to  be  entertained  in  regard  to  bringing  the 
Bible  to  the  test  of  ascertained  facts  1     If  the  account  in  Genesis  be 
true,  to  what  alternative  are  the  advocates  of  the  multiple  origin  of  the 
race  dftven  !     How  does  it  appear  that  the  truth  of  the  Bible  and  the 
unity  of  the  race  must  stand  or  fall  together  1     Does  the  argument  hold 
good,  even  if  the  Mosaic  account  be  considered  a  myth  1 

380.  What  is  the  general  conclusion  in  view  of  the  whole  subject  1 
What  moral  bearing  has  the  doctrine  of  the  unity  of  the  race  !     What 
is  said  of  the  pretended  resemblance  between  the  Ethiopian  variety  and 
the  monkey  tribe  of  animals  1 

CHAPTER  XX. 

381.  What  is  said  of  the   diversity  in  the   manifestations  of  life! 
How  is  life  always  the  same  in  relation  to  its  origin !     Remark  on  the 
wonderful  variety  of  results  worked  out  by  the  vital  force  beginning  in 
a  simple  cell.     How  is  life  always  essentially  the  same  in  its  processes 
as  well  as  in  its  origin  1 

382.  Do  we  know  what  life  is  !     How  does  the  vital  force  differ  from 
such  forces  as  light,  heat,  and  electricity,  in  regard  to  its  power  of  diffu- 
sion !     How  in  regard  to  self-generation  !     How  in  regard  to  the  variety 
of  its  effects ! 

383.  Do  we  know  whether  life  is  one  thing!     What  is  said  of  the 
supposition,  that  the  principle  of  life  resides  chiefly  in  the  blood !    What 
are  the  relations  that  exist  in  living  bodies  between  the  laws  of  chemis- 
try and  mechanics  and  those  of  life!     Illustrate  this  point.     WThat  is 
said  of  the  materials  of  which  the  human  body  is  composed,  and  of  the 
degree  of  heat  in  which  they  are  kept! 

384.  Show  the  difference  in  the  operation  of  heat  on  dead  and  on  liv 


444:  APPENDIX. 


ing  matter,  as  seen  in  the  egg.  How  is  the  power  of  the  vital  force  ex- 
hibited in  the  uniformity  of  the  heat  of  the  body  1  What  is  said  of  the 
changes  going  on  by  the  operation  of  the  vital  force  1  Remark  on  the 
dormant  condition  of  this  force  in  the  case  of  seeds. 

385.  Remark  on  the  analogy  between  the  hibernation  of  animals  and 
Jie  state  of  most  of  the  vegetable  world  in  winter.     What  portions  of 
the  human  system  are  some  of  the  time  dormant,  and  why  ]     What  is 
the  most  mysterious  circumstance  in  regard  to  the  vital  force  1     Show 
how  the  soul  and  the  vital  force  are  two  distinct,  and,  in  some  measure, 
opposing  forces.     In  what  different  senses  are  they  both  present  every- 
where in  the  system  1 

386.  What  is  said  of  the   development  of  the  soul  in  the  body1? 
What  of  the  mystery  of  this  connection  1     What  is  said  of  the  limit  of 
the  vital  force  1     W'hat  facts  show  that  the  endowments  of  life  are  not 
commonly  all  destroyed  at  the  moment  of  death  1 

387.  What  is  the  distinction  between  systemic  and  molecular  death  1 
What  three  great  systems  of  the  body  are  each  essential  to  the  continu- 
ance of  life  !     How  may  death  begin  in  the  circulating  system  1     Give 
the  three  classes  of  causes  by  which  death  may  begin  in  the  respiratory 
system. 

388.  Give  examples  of  death  beginning  in  the  nervous  system.    Illus- 
trate the  fact,  that  death  is  commonly  a  complex  event.     What  is  said 
of  the  signs  of  death  1 

389.  What  is  said  of  the  clearness  of  the  evidence  in  all  ordinary 
cases  in  regard  to  the  fact  of  death  1     In  the  very  few  cases  in  which 
there  is  any  doubt,  what  course  should  be  pursued  1     What  light  can 
physiology  give  us  in  relation  to  what  is  beyond  this  life  1     What  is 
said  of  the  conjectures  on  this  subject  which  its  investigations  may 
prompt  ? 

CHAPTER  XXL 

390.  From  what  two  sources  are  the  rules  of  hygiene  to  be  learn- 
ed 1     How  far  is  a  knowledge  of  physiology   necessary  to   a  proper 
understanding  of  these  rules  1 

391.  What  division    of  topics   should   be   made   in   the   subject  of 
hygiene  1     What  points  in  the  hygiene  of  digestion   have  been  before 
noticed  1     What  is  said  in  regard  to  the  amount  of  food  needed  by  the 
body  1     How  can  we  know  what  this  amount  is  1 

392.  What  errors  are  committed  in  regard  to  quantity  of  food  1     From 
what  causes  is  too  little  food  sometimes   taken  1     What  is  said  of  the 
intervals  between  our  meals  1 

393.  What  is  said  of  eating  regularly  1     What  of  the  different  kinds 
of  food?     What  of  fruits]     What  influence  has  the  mind  on  digestion1? 

394.  What  is  the  general  statement  in  $  625  in  regard  to  the  hygiene 
of  respiration  1     In  what  two  ways  is  the  free  access  of  the  air  to  the 
lungs  interfered  with  1     What  general  rule  is  given  as  to  dress  in  re- 
gard to  the  chest  1     In  what  ways  does  compression  of  the  chest  occa- 
sion disease  1 

395.  Why  ordinarily  is  the  influence  of  defective  aeration  (or  airing) 
of  the  blood  not  appreciated  1 

396.  What  influence  has  muscular  exercise  on  the  development  of 


APPENDIX.  445 


the  organs  of  the  body  ?  How  is  it  a  preservative  against  disease  1 
What  is  said  of  violent  exercise  1  What  is  the  change  going  on  con- 
tinually in  all  parts  of  the  body  ?  What  two  conditions  are  necessary 
to  the  proper  performance  of  this  change  ? 

397.  What  is  said  of  the  discharge  of  waste  matter  from  the  system  1 
What  organs  effect  this  discharge  1     How  much  matter  is  discharged 
from  the  skin  1 

398.  How  is  the  animal  heat  produced  1     How  does  exercise  increase 
it?     What  influence  has  the  quality  of  the  blood  upon  it?     What  is 
essential  to  a  comfortable  temperature  of  the  body  1     When  one  is  too 
much  heated  how  is  the  extra  heat  disposed  of?     What  is  the  object  in 
covering  the  body  with  clothing  and  in  surrounding  it  with  heated  air  ! 
What  is  said  of  cold  as  a  cause  of  disease  ? 

399.  What  are  our  means  of  guarding  against  cold?     How  should 
we  regulate  the  amount  of  clothing  ?     What  is  said  of  guarding  against 
cold  when  the  body  is  in  a  state  of  rest  ? 

400.  What  is  said  of  warming  houses  ?     Why  is  the  influence  of 
cold  in  producing  disease  commonly  so  little  appreciated  ?     Under  what 
circumstances  does  cold  act  as  a  stimulant  ? 

401.  What   rules  should  be   observed  in  the  use  of  cold   bathing? 
What  are  the  best  times  for  using  it?     What  occasions  the  wear  and 
tear  of  the  system  ? 

402.  When  is  most  of  the  repairing  of  the  system  done  ?     What  is 
said  of  the  relation  of  exercise  to  health?     What  effect  has  it  on  the 
muscles  themselves  ?     What  on  the  other  textures?     How  does  if.  pre- 
vent deformity  ? 

403.  What,  are  the  two  causes  of  the  common  deformity  of  the  spine? 
Explain  their  action.     Why   is  this  deformity    found  so  much  more 
often  in  females  than  in  males  ?     How  much  influence  has  posture  in 
producing  it  1 

404.  What   especially   debilitates  the  muscles  of   the  back  in    the 
female  ?     Illustrate  the  necessity  of  having   exercise  varied — also  of 
having  it  general.     What  is  said  of  gymnastics  and  calisthenics  ? 

405.  What  is  said  of  having  the  exercise  habitual  ?     How  does  too 
much  exercise  do  harm  ?     What  is  said  of  having  the  exercise  agree- 
able ?     What  is  said  of  the  hygiene  of  the  senses  ? 

406.  What  is  said  of  the  necessity  of  seasons  of  rest  for  the  brain  ] 
What  significant  fact  in  regard  to  insanity  shows  this  ?     What  is  said 
of  the  conditions  under  which  the  mind  can  perform  much,  labor  without 
harm?     What  is   said  of  overworking   the  brain  during  its  growth? 
What  of  the  manner  in  which  the  child's  mind  is  ordinarily  exercised  ? 

407.  What  two  mental  causes   acting  together  injure  the  health  and 
sometimes  produce  insanity  ?     What  influence  has  the  regulation  of  the 
passions  on  the  health  ?     On  what  portions  of  the  system  do  alcohol 
and  tobacco  chiefly  act  ?     What  is  said  of  alcoholic  stimulants  ? 

408.  Show  how  tobacco  may  act  indirectly  as  a  stimulant.     What 
are  its  effects  on  the  system  ?     To  what  class  of  persons  is  it  especially 
injurious  ?     What  is  the  evidence  in  regard  to  the  influence  of  tea  and 
coffee  ? 

409.  What  is  said  of  emanations  from  filth  as  producing  disease  ? 
Give  a  summary  of  the  chief  causes  of  disease.      Is  disease  commonly 

38 


446  APPENDIX. 


produced  by  any  one  of  these  causes  alone  ?     What  is  said  of  our  con- 
trol over  these  causes  ? 

410.  What  other  causes  of  disease  are  there?  To  what  extent  do 
they  act  compared  with  those  mentioned  in  $  674  1  How  may  we  often 
escape  their  influence  ?  What  is  said  of  the  comparative  value  of  pre- 
ventive and  curative  measures  1  Illustrate  the  prevalent  error  on  this 
point  by  reference  to  consumption.  From  what  does  the  common 
neglect  of  preventive  measures  arise,  and  how  can  this  be  obviated! 


INDEX. 


(The  numbers  refer  to  the  pages.) 


Aberration,  spherical 296 

chromatic 297 

avoided  in  the  eye 297 

Absorption 3 

by  lacteals 58 

by  lymphatics 117 

by  veins 118 

by  cells 128 

Abscess,  concert  of  action  in.  .115 
Aeration   of  the   Blood,    how 

done 86,  102 

how  interfered  with 394 

Agassis,  his  doctrine  of  the 
multiple  origin  of  the  hu- 
man race 369 

Air,  composition  of  and  changes 

in  it  by  respiration 101 

agency  of  plants  in  keeping 

it  pure 104 

necessity  of  a  good  supply  of 

it  to  health 394 

Air-cells  of  the  lungs 86 

importance  of  their  function.   94 
harm  done  in  compressing 

them 95 

Air-sacs  in  birds 100 

Alcoholic  Stimulants,  their  in- 
fluence on  health 407 

Alimentary  Canal,  meaning  of 

the  term 15 

of  different  lengths  in  differ- 
ent animals 60 

Allantois 136 

Aneurism. 65,  69 

Animals,  distinctions  between 

them  and  plants 21 

intelligence  of 357 

their  associations  of  ideas..  .358 
their  mode  of  learning  rela- 
tion of  cause  and  effect. .  .359 


Animal  Magnetism 327 

Aorta 65 

valves  of. 76 

Arm,  bones  of. 192 

Arteries,  why  so  called 72 

why  made  strong 65 

situation  of 67 

how  to  stop  their  bleeding. . .   69 

Articulation  of  the  voice 259 

Arytenoid  Cartilages 249 

Assimilation 15 

Balancing,  action  of  muscles  in.  217 
Bathing,     how   it    should    be 

practised 401 

Baya's  nest 350 

Beaver,  habits  of 350 

Beauty,   regard  to   in  the  ar- 
rangement of  the  muscles.  197, 
207,  214 

Birds,  respiration  of 100 

spinal  column  of 188 

vocal  apparatus  of. 259 

Blood,  its  changes 72 

its  course 73 

variety    of   textures    made 

from  it 110 

cells  in  it 125,  127 

life  in 383 

Bones,  composition  of 37 

uses  of. 170 

insensibility  of. 1 73 

very  sensible  when  inflamed.  155 

marrow  in 171 

various  shapes  of. 173 

of  the  head 175 

of  the  nose 180 

of  the  leg 194 

of  the  foot 195 

Bony  socket  of  the  eye 170 


448 


INDEX. 


Brain 144-146 

how  guarded  from  violence. .  178 

organ  of  the  mind 319 

its  situation  and  connections  320 
size   of  as   measure  of  the 

intellect .....336 

its   development    influenced 

by  mental  activity 372 

hygiene  of 406 

Breast  Bone 88 

Buccinator  Muscle 229 

Calisthenics 404 

Capillaries 65 

their  agency  in  keeping  up 

the  circulation 70 

Carnivorous  Animals 43,  60 

Carbonic  Acid  Gas,  thrown  off 

from  the  lungs 101 

•where    formed 102 

quantity    of    it    discharged 

from  the  lungs 103 

absorbed  by  plants 104 

Cartilage 37 

Cartilages  joining  the  ribs  to 

the  breast  bone 88 

between  the  vertebrae 185 

Camera  Obscura 293 

Carpus 192 

Cataract 295 

Causes,  evidence  that  new  ones 
have  been  introduced  since 

the  original  creation 376 

Cells,  the  true  formative  ves- 
sels  123 

their  shape 124 

seen  both  in  fluids  and  solids .  124 

their  contents 125 

their  selecting  power 125 

their  operation  incomprehen- 
sible  126,  137 

some  make  other  cells 126 

two  kinds  in  the  blood 127 

cells  perform  absorption 128 

and  secretion 129 

fibres  of  muscles  made  up  of 

cells 130 

cells  make  teeth,  nails,  &c.  .131 

how  they  make  nerves 132 

cells  in  the  gray  substance 
of  the  brain.   .  ..132 


all   living    things   built    by 

cells 132,  136 

operation  of  cells  in  the  egg 

during  incubation 133 

Cellular  tissue,  structure  of. 38 

Cementum 181 

Cerebellum,  functions   of. 332 

Change,  constant  in  the  system.  121 
Chemical   laws   controlled    by 

vital 383 

Chest,  framework  of 88 

compression  of 95,  394 

Chin,  possessed  only  by  man. .   30 

Choroid  coat  of  the  eye 295 

Chyle 58 

Chyme 51 

Ciliary  processes 292 

Circulation,  its  apparatus 64 

double 73 

affected  by  emotions  of  the 

mind 239 

hygiene  of 395 

Climate,  influence  of  in  causing 

the  varieties  of  the  race. .  .371 

Cochlea 281 

Coffee,  influence  of  on  health.  .408 
Cold,  depressing  influence  of.  .398 

sometimes  a  stimulant 400 

Cold-blooded  animals 106 

Collar  bone 88,  190 

Concert  of  action  in  formative 

and  other  vessels 110-116 

Conscience,  not  possessed  by 

animals 27,  360 

Consciousness,    its     evidence 

against  materialism 344 

Consonants,   incorrectness    of 

the  common  definition. . .  .264 
nasal  reverberation  the  pecu- 
liarity of  some  of  them. .  .262 

Convolutions  of  the  brain 145 

Convulsions 165 

Coracoid  process 190 

Coronary  arteries 80 

Corrugator  supercilii .228 

Cranium,  bones  of. 175 

Creator,  belief  in  and  knowl- 
edge of  result  of  the  power 

of  abstract  reasoning 360 

Cricoid  Cartilage 249 

Crystalline  lens 295 


INDEX. 


449 


Cuticle 119 

made  up  of  cells 130 

Daisy 18 

Deaf  and  Dumb. .  ..223 


on  the  heat  of  the  body 398 

Experience,  no  transmission  of 

it  in  animals  as  in  man. . . .  362 
Expiration,   mode  of  perform- 
in  g 90 

why  they  are  dumb 267:  Expression,    nerve    of  in   the 

teaching  them  to  talk 268  |          face  paralyzed 157 

Expression  effected  by  muscles. 222 
its  principal  muscles  in  man. 224 

in  animals 236 

Eye,  optical  instrument. 287 

nerves  of 158 

muscles  of 208 

in  itself  inexpressive 226 

its  parts 290-292 

how  it   accommodates  itself 
to  objects  at  different  dis- 


Death 387 

Deformity,  how  produced 402 

Deglutition 47 

Dentals 261 

Dentine 181 

Diaphragm 89 

Digastric  muscle 206 

Digestion 42 

hygiene  of. 53,  391 

Disease,  summary  of  its  causes .  409 

prevention  of 410  | 

Distinct  vision,  point  of 312 

Dog,  his  muscles  of  expression. 237 

sagacity  of 358 

Dome,  principles  of  seen  in  the 

cranium 177 

Domestication,  influence  of.  . .  .371 
Drowning  expla'ned 97 

explanation  of  some  cases  of 
restoration...  ..109 


tatices 298 

its  defences 315 

Eye-brow,  its  agency  in  expres- 
sion  225,  228 


Face,  muscles  of. 202,  228 

its  capabilities  in  expression. 239 

training  of  its  muscles 240 

state   of  its   muscles    after 

death 242 

Facial  angle 336 

Ear,  its  shape 275  I  Far-sightedness 299 


its  bones 276 

its  winding  passages 277 

Egg,  section  of 1 34 

how  cells  develop  the  bird.  . .  135 

Electricity  not  nerve  force 160 

Elementary  substances  in  ani- 
mals and  vegetables 20 

Elbow  joint 194 

Emphasis  some  of  the  princi- 
ples of 269 

Enamel,  structure  of. . . .  .131,  182 

Epiglottis 48,  216,  256 

Erect  posture  of  man 30 

Ethiopian  variety  of  the  race  ; 
evidence  of  its  existence 

in  early  ages 374 

Excretion,  by  what  organs  per- 
formed     118 

Exercise,  influence  of  on  diges- 
tion       54 

on  the  circulation 395 

on   the  development  of  the 
body 396 


Fat,  uses  of. 


Fear,  action  of  muscles  of  face 


in. 


40 
.235 


Fibrillse  muscular 130,  196 

Fingers,  arrangement  of  ten- 
dons in 215 

Fishes,  respiration  of 98 

spinal  column  in 189 

Food,  quantity  needed 391 

regularity  in   taking 393 

Foot,  bones   of 195 

Fordyce,  his   experiments  on 

heat 107 

Formation  and  repair,  by  what 

done 109 

hygiene  of 396,401 

Formative    vessels,    selecting 

power  of HO 

their  concert  of  action  illus- 
trated iu  various  ways.  1 10—116 

are  really  cells 123 

Frog,  changes  from  the  tadpole 

state ..112 


38' 


450 


INDEX. 


cells  seen  in  the  circulation 

in  web  of  the  foot 124 

Frontal  sinus 179 

different  sizes  of 335 

Functions,      distinctions     be- 
tween nutritive  and  animal.   36 

Ganglions 149 

Gastric  juice 50 

Gills,  truly  lungs 98 

Gizzard,  in  birds 62 

Grace,   in   the   action   of  the 

muscles 242,  366 

Gradations,  doctrine  of. 32 

Grasshopper,  respiration  in. ...  99 
Gray  substance  of  brain.. .  132,  147 
amount   of   compared   with 

the  white  substance 3:?3 

dependence  of  mind  on 334 

Gymnastics 404 

Hand,  really  possessed  only  by 

man 29 

variety  of  its  motions 218 

Harvey,  discoverer  of  the  cir- 
culation     72 

Head,  bones  of 175 

Hearing,  apparatus  of 274 

nerves  of 282 

organ  of  in  fishes 284 

in  birds , 285 

Heart,    a   forcing  and  suction 

pump 65 

its  action  illustrated 69 

double 73 

valves  in 74 

its  auricles  and  ventricles  .  .74-79 

front  view  of. 80 

map  of 81 

situation  of 82 

sounds  of 83 

its  sac 84 

its  number  of  beats 85 

insensibility  of  to  touch 156 

Heat  of  the  body,  how  main- 
tained  104,  397 

where  made.. .  .  .105 


its  uniformity  in  man. . .  107,  398 

Herbivorous  animals 43,  60 

Hibernation 108 

Hoarseness,  cause  of. 256 

Honeycomb,  the  perfection  of 

it  as  a  structure 351 

Human  race,  varieties  of 367 

Humerus 190 

Hunger,  cause  of  and  seat. ...   54 
Hydra 23,  26 

cells  in 125 

Hygiene,  how  its  principles  are" 

learned 390 

Hyoid  bone 183,  248 

Ilium 175 

Images  on  retina,  inverted.  . .  .293 
why  the  mind  sees  them  erect.299 
rapidity  of  their  succession.  .314 
minuteness  of. 312 

Immortality  of  man 28 

known  only  from  Revelation .  345 

Insanity,    result  of  disease  in 

the  organization 320 

some  of  its  causes  noticed.  ..407 
influence  of  sleeplessness  in 
producing  it 406 

Inspiration,  mode  of  performing.  90 

Instinct,  more  mysterious  than 

reason 348 

uniformity  of  its  action 349 

its  perfection 351 

exhibited  in  communities  of 

animals 352 

blindness  of  it 354-356 

Involuntary  muscles 162 

not  trained  like  voluntary.  . .  .326 

Iris 294 

Iron,  in  the  blood 20 

carried  in  cells 127 

Jaw,  lower 181 

its  digastric  muscle 207 

Joints,  lining  of 195 

Knowledge,  communicated  only 
by  muscles 222 


sources  of  the  fuel  for  it 105 

on  what  its  amount  depends.  106   Labials 261 

effect  of  exercise  on  it 106   Lacteals 58 

degrees  of  heat  in  the   air          |  Language,  result  of  the  power 
which  the  body  will  bear. .  107  j      of  abstract  reasoning 360 


INDEX. 


451 


Larynx 248-252 

Laughter,    by    what    muscles 

done 224 

Leaves,  discharge  oxygen  and 

absorb  carbonic  acid  gas.  .104 
Lever,  the  three  kinds  of  exem- 
plified in  the  muscles 198 

Ligaments,  of  the  hand 193 

of  the  wrist  and  ankle 206 

vocal ..250 

Life,  its  origin  and  processes..  .381 

its  nature  unknown 382 

differs  from  other  forces 382 

controls  chemical  forces 383 

sometimes  dormant 384 

its  connection  with  the  soul. 385 

Light,  refraction  of. 287-289 

Lips,  their  agency  in  speech. .  .261 
Lime,  in  animals  and  vegeta- 
bles     20 

Lobworm,  respiration  of. 98 

Locomotion,  distinguishing  ani- 
mals from  plants 21 

Lungs,  structure  of 86 

Lymphatic  absorbents 59 

what  they  absorb 117 

Man,  distinctions  between  him 

and  animals.  .27-31,  347,  365 

their  definiteness 337 

Mastication 43 

Materialism,   tendency    to    in 
some    physiologists,    and 

why ". 339 

Meals,  intervals  between 393 

Mechanical  disadvantage  under 

which  muscles  act 203 

Mesentery,  plan  of 57 

Metacarpus 192 

Metatarsus 194 

Mind,    dependence   of  on   the 

brain 319 

rapidity  of  its   communica- 
tion with  all  parts  of  the 

body 321 

training  of  in  the  use  of  the 
senses  and  muscles ......  322 

its  supposed  indestructibility. 339 
sources  of  evidence  as  to  the 
nature  of  its  union  with 
the  body 339-347 


intimacy  of  its  union  with 

the  body 338 

influence  of  mind  on  diges- 
tion  393 

Miracle,  supposition  of  in  caus- 
ing  the   varieties   of  the 

race 377 

Monboddo's  notion 347 

Motion,  spontaneous 22,  142 

automatic 24 

involuntary 162 

Mouth,  agency  of  in  expression. 224 

Mucous  membranes 40 

Muscles 38 

their  structure 130 

mode  of  action 196 

of  arm 199 

of  face  and  neck 202 

of  the  eye 208 

of  larynx 251 

various  shapes  of 210 

combined  motions  of.210, 216, 220 

variety  of  size  of 214 

constant  change  in  action  of.  21 7 
all   knowledge   communica- 
ted by  muscles 222 

skill  in  their  use 324 

their  associated  action 327 

Muscular  sense 220,  308 

Nails,  made  by  cells 131 

Nasal  sounds 262 

National  differences 369 

Nature,  its  inner  beauty  great- 
er than  its  outer 137 

Near  sightedness 299 

Nerves  made  from  cells 131 

terminations  of 150 

healing  of 152 

different  sets  of  for  different 

purposes 1 53 

for  different  sensations 154 

for  different  motions 156 

nerves  of  the  eye 158 

of  the  ear '. 281 

Nervous  system,  distinguishing 

animals  from  vegetables..   23 

its  different  parts 141,  143 

Nerve-force,  not  identical  with 

electricity 160 

Nitrogen,   how  far  peculiar  to 

animals 27 


452 


INDEX. 


Nictitating  membrane 317 

Nose,  bones  of. ISO 

nerves  of 154 

Note,    variations   of,  how  pro- 
duced in  wind  instruments. 246 

in  reed 247 

in  the  vocal  instrument 257 

Oesophagus  described 49 

Objects,  how  they  are  pictured 

on  the  retina 292 

how  the  eye  is   adjusted  to 

their  different  distances. .  .298 
how  we  estimate  their  motion. 3 13 

Optic  nerves,  crossing  of 305 

Organ,  flute  stop  of 245 

Organic  life,  distinguished  from 

animal  life 24,  139 

Organized     and     unorganized 

substances 13 

difference    between  in   per- 
manency     15 

in  regularity 17 

in  size 19 

in  structure 20 

organized  built  by  cells 136 

Ostrich,  respiratory  apparatus  of.  1 00 

Oval  form  of  head 373 

Oxygen,  absorbed  by  the  lungs. 101 
exhaled  by  plants 104 

Pacinian  corpuscles 151 

Pain,  a  warning  of  danger. . .  .154 
expression  of  the  courten- 

ance  in 225 

Papillae  of  the  skin 120,  150 

Patella 183,  194 

action  of  the  muscles  on. . .  .205 

Pelvis 173 

Perspiration,    influence   of   in 
enabling  the  body   to   bear 

very  hot  air 108,  398 

Petrous  (rock-like)  bone. . .  180,  275 

Pharynx 47 

Phrenology 334 

Plants,    distinctions    between 

them  and  animals.  .......   21 

Pleura 88 

Plexuses  of  nerves 149 

Prognathous  type  of  head 373 

Pulse,  cause  of . .   65 

Pylorus 51 


Pyramidal  type  of  head 373 

Quickness  of  action  the  chief 
object  in  most  muscles 200 

Radius 192 

Rage,    action   of   muscles    of 

face  in 234 

Reaction  against  cold,  how  pro- 
duced   400 

Reason,  not  confined  to  man..  .348 
of  a  lower  order  in  animals.  .362 

Reasoning  abstract,  peculiar  to 

man 27,  359 

source  of  language 360 

of  a  belief  in  a  creator 360 

of  knowledge   of  right    and 
wrong 360 

Reed  instruments 247 

Reflex   action  explained 162 

Respiration,  its  apparatus 86 

mechanism  of 88 

hygiene  of 394 

Respiratory  apparatus  of  fishes.   98 

of  insects 99 

of  birds 100 

Retina,  structure  of 296 

images  formed  on 292 

Revelation,  its  evidence  against 

materialism 345 

testimony   of  in    regard  to 
unity  of  origin  of  the  race. 378 

Reverie,  involuntary  action  of 

muscles  in 167,  327 

Ribs,  arrangement  of. 88 

movement  of  in  respiration..   92 

Ringentes  (muscles) 237 

Robinet,  his  doctrines 31 

Sacrum 173 

Salivary  glands 45 

Scapula 190 

Scintillantes  (muscles) 237 

Secretions,    formed    from    the 

blood 116 

by  cells 129 

Sebaceous  glands 120 

Seeing,  a  process  that  is  learn- 
ed    305 

Semicircular  canals 278,  282 

Sensation,   distinguishes    ani 

mals  from  plants 22 


INDEX. 


453 


a  compound  act 141 

what  is  necessary  to  it 142 

special  and  common 154 

Sensibility,  various  in  different 

parts 155 

Serous  membranes 41 

Silex  in  plants 20 

Silkworm,  its  changes  illus- 
trating concert  of  action 
in  the  formative  vessels..  ..113 

Skeleton,  description  of 173 

Skin,  structure  and  functions  of.  1 19 

hygiene  of .  , 397 

great  sensibility  of 155 

Somnambulism 330 

Song,  how  it  differs  from  speech. 268 

why  more  difficult 270 

Soul,  its  connection  with  the 

vital  force 385 

Sound,  how  produced  and  trans- 
mitted  272 

difference    in    transmission 
through  solids,  liquids  and 

gases .273 

Sound  musical,  how  it  differs 

from  noise 271 

how  its  note  is  varied  in  wind 

instruments 246 

how  in  reed 247 

how  in  the  vocal  instrument. 253 
Speech,  instruments  for  imita- 
ting it 264 

Species,   how  it   differs   from 

variety 371 

Spinal  column... 88,  173,  183-187 

of  birds 188 

of  fishes  and  reptiles 189 

deformity  of,  how  caused. . .  .403 

Spinal  cord  or  marrow 153 

its  functions 164,167 

Squinting 209,  30 1 

Stammering 267 

Stereoscope 302 

Stomach,  used  in  two  senses. . .    15 
distinguishing  animals  from 

plants 21 

its  three  coats 41 

its  muscular  coat 51 

difference  of  this  organ  in 

different  animals 60 

Stigmata 99 

Superbus  muscle 230 


Sutures  of  the  skull 177 

Sweat  glands.. .. . . 120 

Sympathetic  system  of  nerves . .  169 

Talking,  how  learned 265 

Tarsus 194 

Tailor-bird's  nest 350 

Tea,  influence  of  on  health 408 

Tear  apparatus 316 

Teeth,  different  kinds 43 

structure  of. 131,  181 

nerves  in 151 

why  second  set  needed 182 

Tendons 38,  197 

Temporal  bone 177 

Thaumatrope 315 

Thigh   bone 194 

Thirst,  cause  of  and  seat 55 

Thoracic  duct 59 

Throat  disease 259 

Thyroid  cartilage 248 

Tobacco,  its  influence  onhealth.408 
Togg'e-joint,  exemplified  in  the 

joints  of  the  body 217 

Tongue,  its  variety  of  motion.,210 

its  agency  in  speech 260 

Training  of  the  muscles   and 

the  senses 325 

Tubuli  of  the  nerves 147,  152 


Ulna 


..192 


Valves  of  the  heart 74,  78 

of  the  aorta 77 

of  the  veins 67 

Vanishing  movement    in    the 

voice 269 

Veins,  structure  and  situation 

of. 65 

why  the  blood  accumulates 

in  them  at  death 71 

what  they  absorb 118 

Ventilation,  effects  of,  defective.  103 

Ventriloquism 271 

Vertebrae  described 184 

Violin,  imitation  of  the  voice 

with 257 

Vision,  apparatus  of 287 

why  commonly  single 300 

sometimes  double 301 

vision  mostly  a  mental  pro- 
cess ..  ..309-311 


454 


INDEX. 


how  the  figure,  size  and  dis- 
tances    of     objects     are 

known 305-308 

mistakes  in,  how  rectified. .  .308 

Visual  angle 305 

Vitreous  table  of  the  bones  of 

the   skull 176 

Vocal  ligaments 250 

Vocal  muscles,  education  of. .  .258 

trained  by  the  ear 258,  266 

Voice,    chief  means    of  com- 
municating knowledge 222 

its  apparatus  a  musical  in- 
strument   243  ! 

articulation  of. 259 

Waste  of  the  system,  by  what 

organs  thrown  off.. . .  118,  397 


influence  of  its  retention. . .  .397 

Wasp's  nest 352 

Water-scorpion,  respiration  of.   99 
Weeping,   action  of  the  mus- 
cles in 225 

Whale,  arrangement  for  catch- 
ing its  food 45 

its  reservoirs  for  containing 

arterial  blood 97 

Whispering,  how  done 263 

White  substance  of  the  brain.  .147 

office  of 334 

Wind  instruments 245 

Zoological  provinces 370 

Agassis's  analogy  in  this  re- 
spect fails  in  regard  to 
man 375 


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